The introduction lacks a summary for the adventure. This would be very helpful in telling the GM what to expect and lay down the flow of the adventure.
The first level of Radoc's Lair comes across as whimsical, and may set the wrong tone for the adventure if it becomes more dangerous deeper in. This comes across in the nature of the notes the rats are carrying, retrieving the toy miniquest and the disposition of many of the 1st floor inhabitants.
Secret door detection should be same for active Wisdom checks or passive Perception (DMG p103). Remember that Investigation (Int) is used to find the mechanism to open the door and it is generally set at the same DC as to find the door.
Don't use a random number pick by PC to determine if a secret hatch is trapped. Either use a secret roll with a set number (1 in 10) or affix which ones are trapped. Ensure PCs have some sort of warning or way of detecting the presence of the traps (note: consider that the Mongrelmen would have some sort of indicator/mark so they don't use or know how to not trigger the trap when using them). This should feel fair, not arbitrary - if the PCs trip a trap it should feel like it was their own fault for not latching onto the warnings they were given, rather than a random bolt from the blue).
The room descriptions are haphazard in the order things are presented. Personally, I would order them thusly:
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NAME OF ROOM
Description (keep to a 3-5 sentence paragraph. If some details require further investigation or have a triggering event, break them into a separate paragraph, preferably proceeding "Development"
Initial Setup. Describe the starting state of the room. Work from most important details to least.
Development. Cover likely events, again work from most important details or likely actions to least. Separate paragraphs for different events, if needed. Keep things short - 3-5 sentences where possible. If you find yourself going longer, looks for ways to simplify events or leave the more nuanced details in the hands of the DM to resolve.
Monsters: monster name in bold. Include a special rules/notes in following paragraphs.
Hazards: name in bold, then method of detection then how it works. Be sure to note if the trap can be reset.
Treasure: name in bold, any special notes about it.
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Example:
1. ENTRANCE TO RADOC'S LAIR (Level 1)
The party enters a natural cave that slowly transforms into hewed stone that screams of habitation. The dark cave opens into a wide room lite by smokeless torches and glowing gems. The floor and walls are made of polished stone, decorated with strange glyphs and mushrooms. Lounging on a large wooden chair is a two-headed mutant that is vaguely troll-like.
Lax Guardian. The mutated troll Gri'gor guards the entrance to the lair. He is wary of the approach of non-mongrelfolk and demands characters speak the password before letting them pass. Hidden among the mushrooms flanking the main entrance are two relatively docile shriekers. As a last resort, there is a concealed stone door that can block the entrance to the complex.
Getting By. The password Gri'gor is looking for is "Hail Radoc". However, he can be encouraged to be prompted to give the PCs the password with a successful Charisma (Deception) or Intelligence (Investigation) check against DC 15. He can also be misdirected if the party shows interest in seeing Gri'gor's room, and he will happily lead the characters to room 2 (Gri'gor's quarters) to show off his flesh collection, which afterwards he will let the party enter the complex freely (forgetting they never gave him the password).
-----If the party gives Gri'gor the wrong password, he pretends that it was the correct one and attempts to lead the party to room 1a (detention room) and trap them there. PCs that do not trust Gri'gor escorting them can make a DC 8 Wisdom (Insight) check to know Gri'gor is not being honest about where he is leading the group.
Fighting Through. Gri'gor is bored, but will defend himself if attacked. As soon as he is able, he will move and use a bonus action to prod one of the two flanking shriekers to sound an alarm. He will attempt to corral attackers into room 1a (detention room) to trap the party and get the elders to deal with the party. If any party member attacks him with fire, he will concentrate his wrath on that individual. If Gri'gor is reduced to 1/2 hp or less, he attempts to flee to room 10 (community room) for help or backup. If reduced to 10 hp or less, he attempts to close the entrance's stone door (as a free action), trying to slip inside before it closes.
The Stone Door. Concealed above the main entryway is a multi-ton stone door, which can be discerned with a DC 16 Wisdom (Perception) check or passive Perception. The concealed lever to activate the stone door is on the right-hand side of the entrance and can be located with an DC 16 Wisdom (Investigation) check or carefully searching the correct area. Gri'gor is aware of the lever's presence, but will only activate it as a last ditch defense - generally when reduced to 10 hp or less. Once activated by the lever, the stone door drops to block the entrance (at Initiative 0, if in the middle of combat) and can only be reopened from the inside (see room X*, level 3), destroying it (Damage Threshold 15, 300 hp) or with a combined Strength score of 100 or more.
Glyphs. The glyphs are harmless gibberish letters of the Giantish language, giving off dim light for 5 ft. They can be disrupted for 1 minute with a targeted dispel magic but have no other effect.
Monsters: Gri'gor the mutant troll. Gri'gor has been mutated so he has two heads and his body is twisted and hunched. His two heads give him advantage on Wisdom (Perception) checks and Initiative checks, but he has disadvantage against being blinded.
Hazard: two shriekers, one on each side of the entrance way. These are fed regularly and normally do not activate merely by passing them. If actively prodded, damaged or an individual is dropped to 0 hit points within 5 feet of them (including Gri'gor), they will let out a wailing cry for 5 rounds, alerting anyone within 300 feet of the entrance of the approach of hostile individuals and puts the complex on high alert.
Treasure: Gri'gor has a small belt pouch with a pair of bone dice (worth 1 gp), 10 sp and a folded, crude map of areas 1 - 12 of the first level with the word "scared" written in Giantish on it.
* Where is this winch? I couldn't find it on the map or key for level 3
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Specific Room notes
RADOC's LAIR, LEVEL 1
1) The detention room should have it's own key. This key can explain how characters are restrained and how they are dealt with.
2) Leave out the section about defeating Gri'gor being the key to the art treasure. A burglar PC or haggling could possibly result in the PCs gaining this; it's existance should be noted and the "Development" section for the room can touch on stealing/haggling or taking the treasure from the room. As a published adventure, it may be preferrable to define the art objects, especially if they can be used to give further insight to what Gri'gor considers "art".
3) No need to mention sneaking up on the Mongrelfolk, that should evolve from play and the DM will have their Perception scores from the commoner stat block. Consider reframing the tactics "The mongrelfolk are generally passive and though they may be surprised at the character's presence, will not attack unless provoked. Mongrelfolk prefer to retreat towards the escape hatches or room 15 (Safe Room) rather than fight, but family leaders will do their best to protect their charges from harm, fighting to cover the remainder of the family's escape". Similar treatment of the mongrelfolk's treasure - simply state that taking a minute to search the dwelling and making a successful DC 15 Intelligence (Investigation) check has a 1 in 10 chance of turning up a gem or piece of jewelry worth 1d4 x 10 gp would be what I suggest (since the mongrelfolk aren't the fighting type, weapons seem unlikely and would more likely tied to the stat block anyway).
4 & 5) I think these rooms would benefit from using the example room order from above, especially room 5. Also, having two spices with the same letter throws confusion into the puzzle - I would change the keyword to "scared". Finally, why is there a weapon/treasure hidden here? The presence of this puzzle would make some sense if there is a reason why someone would hide this object here.
6) Is the presence of this ice magical, or was it brought in from elsewhere? With an active rhemoraz in the room (whose heat melts ice), either it has been here a short time or the ice is being restocked regularly in some manner. This room might make more sense if the rhemoraz starts unconsious (having been captured and KO'ed on the last trip to retrieve ice) and awakens after a short time (1d10+1 rounds seems good). This would also better explain why it acts aggressively when encountered.
8) On the map, this is marked as the Privy. As by description of the waterfall, why does the waterfall not attack the Mongrelfolk? Are the mongrelfolk/Gri'gor aware of its presence? Why has no one else taken the lute? There should be some sort of indication prior to the approach of the waterfall that something is slightly off - remnants of bone, offerings to the water wierd, an unusual flow or disturbance in the water, etc.
9) On the map, this is marked as the Community Room. As by description of the privy, seems like a rather long distance for the Otugh to reach a tentacle and should probably be left out.
10) On the map, this is marked as the Waterfall area. as by description of it being the community room, consider if the party has reached here without being noticed yet - would there still be anyone in the room, and what would they be doing?
11) WHY is this puzzle here? It makes more sense that Gri'gor would flee to the Community Room, making the north corridor the "main entrance" with the stone door that runs alongside the dwellings and on to the Community room rather than making this the primary enterance. This room is EXTREMELY confusing. You need an overview of the puzzle, then dig into the details. Seems likely this would be a way for Radoc to test newly created Mongrelfolk to see if they are worthy of being added to the community. If the party has been peaceful, consider that the other Mongrelfolk may urge the party to undertake this test to prove them as "worthy" of being friends. If this is changed to a side entrance of sorts, entering the room should automatically trigger the trap/puzzle. If I get the gist of this puzzle, this would be my write-up.
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11) STATUE OF RADOC TEST
In the middle of this room is a large statue of a tall, thin old man whom is smirking. Its eyes twinkle and seem to follow you wherever you go in the room. The entire statue is marble. The floor is marble, with a checkered pattern of white and black stones.
Test of Worth. This ancient room was designed to test the worth of new converts or other sentient additions to the community. If any character removes one of the two gems at the base of the statue, the trap activates.
If the party examines the statue, read or paraphrase the following:
A narrow 5-foot band of blue tiles surrounds the mustached statue. At the base of the status is a single word in common, “Choose,” with a black and white stone on each side of the word.
The Test. If one of the two stones are removed, all doors slams shut, the characters must complete the statue's puzzle to exit. The objective of the puzzle is to step on all the the tiles of a single color, which ends the trial and reveals a reward. Failure triggers a phantasmal killer to punish the unworthy.
The Tiles. Each tile is approximately 5 ft. square, and there are 32 tiles of each color (black and white) arranged like a chess board - the blue tiles are not part of the puzzle. Stepping on a colored black or white tile causes a swirl of light to emate upwards and the tile continues to glow, accompanied by a distinct note of music (cheerful for white, ominous for black). As long as the characters continue to step on the same color the additional tiles of that color light up as well. If any character leaves and steps on a tile that is already lit, it stops glowing. If a character steps on an opposing color, ALL the currently lit tiles stop glowing and the new tile begins to glow.
---- A character can hop across from one colored square to another with a successful DC 6 Strength (Athletics) skill check, or a character can move from corner to corner with a successful DC 6 Dexterity (Acrobatics) skill check, both using up 5 feet of movement. Normally, you should not require a skill check unless the phantasmal killer is active.
Phantasmal Killer. If a character steps on a tile that does not match the stone that was taken from the statue or does not move to another square within 3 rounds, a phantasmal killer is activated against that individual, taking the image of the statue animating and moving to crush the PC, speaking "you have chosen poorly!" as it does so. The attack stops if the character corrects their mistake and activates the tiles of the correct color or makes a successful DC 15 Wisdom save against the spell. However, the phantasmal killer will reactivate a PC continues to step on the wrong color or dawdles for 3 rounds or more.
Solving the Puzzle. Once all 32 tiles of a given color are activated, a tune formed from the collective notes plays, the tiles stop glowing and the phantasmal killer dissapates. Furthermore, an unlocked, ornate wooden chest appears at the foot of the statue. Within will be found one bloodstone (25 gp) per character. If these bloodstones are presented to the Mongrelfolk and neither side is hostile, the mongrelfolk will accept the individual as a worthy member of the community. If the Mongrelfolk see the gemstone but it is not given to the community, the Mongrelfolk will become unfriendly and berate the character as blasphemous until the gemstone is handed over.
----This test can only be activated once per day. Additional attempts to reactive the test will have no effect.
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12) Why is this room here, other than a forced encounter? How do the inhabitants get past the spiders, and why do they allow them dwell here? Touching on the mongrelfolk feeding these like pets or using them as guardians would make sense (might want to indicate that Gri'gor and Mongrelfolk make the Animal Handling check automatically, should the party gain a guide somehow). At the very least, there should be a safe path through the room the Mongrelfolk regularly use (perhaps a Survival, Perception or Investigation check would reveal it to PCs).
13) Consider shortening the room description, otherwise no change needs to be made to this room
14) Personally, I'd remove the Oche Jellies from this room, or have them sealed in the jars and only released if someone destroys or opens the seal on the jar. The shriekers are superfluious, and should be removed altogether. Not every room needs to have something happening in it; "empty" rooms can create a breather/area to rest or reorganize or as a way to build/moderate tension. I think this room should be the primary prep room and where "common" Mongrelfolk bodies are laid to rest (after being rendered to bone for easier storage). Consider having small nooks/niche about the room where the remains are stored and later revered/visited.
14a) Consider having the doorway to this room be hidden, and be where the prepared corpses of distinguished Mongrelfolk are kept, buried like kings. This could be where any treasure is likewise stored.
15) I think this room should be accessed from the Community room. Also, WHERE did the guide come from, and WHY are you waiting until here to reveal them as a spy/turncoat? This room should be rewritten with a default description as if the complex were not on alert, with the "Development" section covering difference if the complex is on alert and if Mongrelfolk have retreated to the area. Consider that if a fight breaks out in the Community room, if no one has gone to the safe room yet that one of the attacker may go retrieve the Twisted Golem to aid in the Community room fight (if Mongrelfolk have retreated to the safe room, this, of course should not happen).