That Night Scavver isn't going to reach the PCs unless it sneaks up on them. This is a very
Jaws setup, imo - for it to be effective, the victims (PCs) shouldn't see the attack coming until its too late. Its night-dark skin, as well as skimming along the asteroid should allow it to get close unseen before striking, and at the party's current level, it should definitely be using hit-and-fade attacks if you want this to be a boss-level battle. As soon as the PCs go toe-to-toe with the scavver, the battle will be over quickly. If you're shooting for a cinematic encounter, you want the scavver to be fighting on its terms (hit and fade) and make the battle about the PCs trying to turn the situation so they can gang up on it at close range without it being able to get away.
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I would have the party first approached by the gray scavvers, whose inexperience in hunting have them approach visibly, letting the party get a couple shots off and realizing there is a danger. Meanwhile, the night scavver should be approaching stealthily from a direction where line of sight is blocked by the asteroid, and/or using the surrounding blackness of the void to hide its approach (it does have Stealth +8). It should be maneuvering to target a lone character, or a somewhat distant part of the PC's boat or wreck. This likely means a round of fighting with the grays occurs before the night scavver makes its first attack.
Its first attack should be against either the PC's vessel or a passing attack at the lone PC (if it surprises the party, they won't be getting reactions so it can move in, bite and move away) - favoring those on the smaller rock hopper, disappearing into a crater or around the curve of the asteroid after making the initial pass. As soon as possible, it takes the Hide action.
From there, it repositions, then moves to attack isolated PCs or their vessel. This may mean it takes one or more rounds between attacks as it maneuvers to strike again from an unexpected angle. If it has successfully hidden before it makes another passing attacks - especially if there is more than a round between the last attack, I would rule that it again had surprised the victim(s), denying PCs the ability to hold actions to strike it when it returns (as if a new combat was initiated, against surprised characters). In between the night scavver's attacks, the gray scavvers should be making opportunistic attacks
This could result in a running battle, with the night scavver making hit and run attacks as its gray spawn run interference to keep the PCs from fully focusing on the big one. Its primary goal should be to wear down one "easy" target, swallow it and get away before others can stop it. This could become a sort of chase - the night scavver targeting the rock hopper (and crew) before they can get back to the rest of the group. Depending on how far away from the others, you might want to have rounds of dread - a glimpse of something night-black slipping against the stars, a gleam from its dead, black eye momentarily mistaken for a star, a scrabble of displaced rocks as the unseen night scavver skims over the asteroid's surface - to create menace between these attacks. The night scavver shouldn't stay in protracted combat unless it's got someone cornered.
Also, don't be afraid to have the night scavver slip away if gravely injured - 1/4 hp or so; it and its preceding spawn can become recurring threats showing up when the party leasts expect it, possibly picking of NPC crew in the dead of night or tales of it doing so to other crews - I would think a future interesting encounter would be to have it show up when the PCs are in a fight with another ship, and it starts picking off members of the
other enemy crew, before threatening to come after the PCs, or just swims away for another encounter later, temporarily sated and with PCs just knowing that next time, it'll be coming for
them.
If you want to scare the bejeebus out of your PCs, to open this encounter, you could have a gray scavver position to attack a lone PC, only for the night scavver to swoop in from an unseen direction and shred the gray in a single bite (the punishment for the gray to poach the night's target), before swimming off and vanishing before anyone can react. The encounter runs from normal from there.
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If you want to make this a REAL boss, I suggest adding Swim-by attack (its movement doesn't provoke attack of opportunities) and give it 3 Legendary actions (+2 CR):
Bite: The scavver makes a bite attack. If the target is medium or smaller and hits the target's AC by 5 or more, it Engulfs the target. An engulfed target takes 9 (2d8) acid damage at the start of each of its turns. (I'd also suggest adding the Engulf to the regular bite).
On the Move: The scavver moves 15 feet
Tail Thrashing: The scavver makes a tail attack at +8 to hit with a reach of 10 feet. A target hit by the tail attack takes 16 (2d10+5) bludgeoning damage and must make a DC 16 Strength save or be knocked prone.
Into the Dark: If the scavver is at least 20 feet away from an enemy and outdoors, it takes the Hide action, disappearing into the blackness of the night sky. If the scavver attacks or is hit by an attack, it is no longer hiding.
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Engulfed
- The target is inside the creature, and moves when the creature moves.
- The target is blinded and restrained, has total cover against attacks and other effects outside the creature.
- If the engulfing creature takes damage in excess on the table below based on its size, the engulfing creature must make a DC 21 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 5 feet of the engulfing creature.
- If the engulfing creature is slain, the swallowed creature is no longer restrained and can escape from the corpse by moving out of the creature’s space, emerging prone. The area the dead creature takes up is treated as difficult terrain.
Size | Expel Dam | Capacity | Size |
---|
Tiny | 1 | — | ¼ |
Small | 3 | ¼ | ½ |
Medium | 5 | ¼ | 1 |
Large | 10 | ½ | 3 |
Huge | 20 | 2 | 5 |
Gargantuan | 30 | 4+ | 8 |
Capacity is the number of medium-sized targets the creature’s gullet can hold.
Size determines the size of a creature for the purpose of being held in a creature’s gullet (for example, a Small creature counts as ½ a medium creature)