Let's assume all that is true. What are your design solutions for this? What do you do in the level 17, 32 page adventure to help the GM run a successful high level adventure?
Explain the motivations, tactics (including round by round) tactics of the bad guys to start with.
DMs lack experience remember. That's the main issue. Helping them run high level encounters is the place to start.
Here is an example of an encounter in the adventure I was talking about above:
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Amaz - Githyanki Gish
Medium humanoid (gith), lawful evil
Armor Class 20 (mithril half plate armor, shield +1)
Hit Points 172 (26d8 + 55)
Speed 30 ft.
STR17 (+3) DEX 16 (+3) CON 14 (+2) INT 18 (+4) WIS 15 (+2) CHA 16 (+3)
Saving Throws Con +7, Int +8, Wis +7
Skills Insight +7, Perception +7, Stealth +8
Senses passive Perception 17
Languages Gith
Challenge 14 Proficiency Bonus (PB) +5
Innate Spellcasting (Psionics). The githyanki's innate spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). It can innately cast the following spells, requiring no components:
At will: mage hand (the hand is invisible)
3/day each: jump, misty step, nondetection (self only)
1/day each: plane shift, telekinesis
Spellcasting. The githyanki is an 13th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). The githyanki has the following wizard spells prepared:
Cantrips (at will): blade ward, light, mind sliver, firebolt
1st level (4 slots): magic missile, shield
2nd level (3 slots): mirror image, levitate
3rd level (3 slots): counterspell, fireball, haste, major image, fly, dispel magic
4th level (3 slots – 2 remaining): dimension door, greater invisibility*
5th level (2 slot): Steel wind strike, mislead
6th level (1 slot – 0 remaining): True seeing*
7th level (1 slot – 0 remaining): Teleport
War Magic. When the githyanki uses its action to cast a spell, it can make one weapon attack as a bonus action. The Githyanki can use its sword as both an Arcane focus, and in place of any Somatic components
Actions
Multiattack. The githyanki makes two longsword attacks.
Longsword. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) slashing damage plus 18 (4d8) psychic damage.
Notes: Amaz has a
Contingent mirror image set to trigger when a creature that can see him targets him with an attack.
Captain of: Githyanki Skiff – AC 15, 150 HP Damage reduction 10 – Immune Poison and Psychic.
Githyanki Helm – allows casting of
Wall of Force 3/day encompassing the upper level by a creature with psionic ability. Once active, it can be raised or lowered by operating a lever (use an object action). Amaz usually leaves this task to his
Simulacrum
The Skiff is crewed by Amaz, his Simulacrum (see below) and half a dozen Githyanki Warriors.
Here are Amaz's tactics, and the set up for the encounter:
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E1 and 2 (multipart encounter)
An Astral Storm approaches, and Captain Grogbeard elects to take shelter near the colossal corpse of a Dead god. Unfortunately, this corpse also acts as the base of operations for some mean spirited Gith pirates.
All Gith are under the effects of a
nondetection spell cast innately using their psionics.
Ki’taa’lek, (Githzerai Kith’raak) seeing the PCs ship approach, orders Amaz (Githyanki Gish) to attack and board the PCs ship while the Kith’raak watches on from the back of his Red dragon Crimsontide. Ki’taa’lek is wise to the ways of adventurers, and figures he’ll wait out the battle to begin with and let the PCs weaken themselves and expend energy on his underlings. In addition he does not want to risk riding Crimsontide into the strong winds of the Astral Storm.
The Githyanki ship speeds out to attack as the PCs pass within 200’ of the Corpse; the Kith’raak and Dragon remain on the Corpse, perched just on the Dead God and watching the battle unfold.
Amaz finds piloting his Astral ship (The Omnipresent Eye) a chore, so he tasks this job to a long since depleted and dejected
Simulacrum of himself, (AC 17, 50 HP remaining). The Simulacrum is out of spell slots, but can still cast the identical cantrips to Amaz. Both have a distinctive red mohawk (although the
Simulacrums is ratty and unkempt from months of abuse and neglect). The Simulacrum takes the Dodge action each turn it’s not steering the ship (as per its orders) and largely avoids the battle.
Before the attack, the
Simualcrum raises the
Wall of Force, protecting the crew on deck from most attacks as they approach. The Githyanki ship is much smaller and much faster than the larger PCs ship, and it catches up to them in 1 round, closing to within 15’ and launching grapples. If the PCs can reduce the ship to 0HP before that time, the Githyanki are lost to the Astral storm.
Tactics
Amaz casts
major image as the ship departs (using a 7th level slot to make it permanent) of himself under the effects of a
mirror image and
globe of invulnerability spell issuing orders on the front raised deck of the ship (hopefully luring the PCs into attacking the illusion). The canny Githyanki then casts
greater invisibility, remaining in his quarters below on the upper level, invisible and Hiding (Perception check 18 to find – all PCs have disadvantage on perception due to the darkness and the wind so are at -5 to passive) and watching the battle unfold through a window.
Once within 15’ Amaz and 6 x Gith warriors
misty step over to the PCs ship, and attack, while the Gish protects them with
counterspells, offensive magic and
dispels.
On initiative count 20 on the first round of battle after the Gith grapple the PCs ship, the storm hits. On this (and further counts of initiative count 20) the following effects happen, in addition to dim light and heavy winds (see the DMG) that also affect ranged spell attacks:
Round 1: All creatures must attempt a DC15 Dexterity save or be knocked Prone.
Round 2: All creatures must attempt a DC15 Intelligence save or suffer the effects of the Astral Wind
Round 3: The storm dissipates, heavy wind only. At the end of this round, the Kith’raak casts Blur using his psionics, and his dragon takes its readied move action to move 80’ forward (and down) under the PCs ship.
Round 4 The dragon dashes and moves another 160’ positioning itself 80’ from the ship and below it, enabling for a surprise attack from under the vessel the following round while the rider takes the Dodge action.
Ki’lek – Githyanki Kith’rak
Crimsontide – Young Red Dragon
E1: 21,300 (14,200)
E2: 28,600 (14,300)
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The goal is to lure the PCs into targeting the monsters (and not the ship), because Wall of Force protects the monsters, while not stopping the monsters from teleporting on to the PCs ship to attack in return, or stopping Amaz (the Gish) from doing what he wants to do (who is making use of his non detection, greater invisibility, and the cunning use of a permanent illusion spell, to waste PC resources by expending those resources on his wall of force, or by targeting his illusion, or by simply being counterspelled, and buy himself several rounds to do some real damage to the PCs in return).
You've gotta run high level encounters smart. Not just as bags of HP.