D&D 5E Master Lich Challenge

Cantrips (at will): Blade Ward, Booming Blade, ray of frost
1st level (4 slots): Absorb Elements, Feather Fall, shield, thunderwave
2nd level (3 slots): Misty Step, detect thoughts, invisibility, mirror image
3rd level (3 slots): Blink, counterspell, dispel magic, fireball
4th level (3 slots): Polymorph, dimension door
5th level (3 slots): Wall of Force, Passwall
6th level (1 slot): disintegrate, Mass Suggestion
7th level (1 slot): finger of death, Reverse Gravity
8th level (1 slot): Maze, power word stun
9th level (1 slot): Wish

Blade Ward is good for a lich, it will basically double the amount of HP it has against your heavy melee units at the cost of one legendary action.
Booming Blade is a control Cantrip that punishes people trying to move in combat, useful to keep people close to you or away from you.
Absorb Elements is like shield, but for elemental damage, also a reaction, therefore one of the most useful level one spells ever.
Feather Fall is part of the general "divide and conquer" theme. This lich has no less than two ways to make people fall, and it's basically a contingency plan if they somehow manage to suck him into his own trap.
Misty Step is a bonus action teleport. Good use of action economy, and a great escape tool.
Blink is a great movement spell that lets the lich "teleport" around the map.
Polymorph The lich can now become any other creature of CR21 or less. Unfortunately, this spell is limited to beasts, but at least it's extra hit points and and a way to extend the encounter.
Wall of Force Divide and conquer. If the wizard is several squares off from the rest of the party, get next to him (you have several options here), cast the spell, and enjoy the one-on-one spell battle cage match. Wizards are the only ones who can dispel this wall(with disintegrate no less), and he will be busy trying not to die fighting a legendary monster by his lonesome.
Passwall Uses for this include opening the vat filled with deadly gas, or making a giant hole in the ground so that the melee people can't get next to you.
Mass Suggestion Tell the entire party to "Go home to mommy where it is safe" Statistically speaking, one member of the party is going to fail this save, which is great because that is one person that the lich doesn't have to fight, until the rest of the party snaps them out of walking away somehow.
Reverse Gravity I am betting most of your party can't fly, or at least can't fly without a spell. This will keep a part of the party out of their optimal combat range. Also can be combined with passwall to simply eject part of the party from the fight.
Maze There is no saving throw on Maze, just an INT check. The barbarian or the fighter is basically out of the fight, and maybe one of the clerics could be edged out for a few rounds too. Don't use this first, save it for after one or more of the other party members are taken out of the fight.
Wish It's Wish, what do you want to happen? That happens. Deadly options include forcing one of the PC's to fail a saving throw. Control options include creating a ball of solid adamantine around one of the clerics.

Also the lich should have like 10 Contingency spells set up. Which is an entire other onion's worth of layers of complexity.

I like to use the lair, and not just lair actions, quite a bit.

Can you tell us more about the Liche's lair?

Mouseferatu said:

They'll be 14th or 15th level by the time the fight happens.

Human champion fighter.
Dwarven totem barbarian.
Half-elven evoker wizard.
Human light domain cleric.
Human tempest domain cleric.

The fighter and barbarian are both very mobile (including the feat). Fighter is a two-weapon sort. The wizard is, well, blasty, as is the tempest cleric. The light cleric is the primary healer, though the other cleric does a lot of that, too.

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so maybe try to polymorph the figter and barbarian into things with less then 100 HP and then power word kill

Mouseferatu said:

Okay, fair point, but I assume the lich prepares such spells when it's not expecting to face combat. I'm looking for the list for a lich who knows full well it's going to have to obliterate some high-level interlopers (aka PCs).

Sorry for not being clear about that from the start.

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Would it not depend on the capabilities of the party that the lich has uncovered?

I.e. tailored to the group it knows it has to face.

Edit: However, in the spirit of the question, let me think until this evening.

Mouseferatu said:

Okay, fair point, but I assume the lich prepares such spells when it's not expecting to face combat. I'm looking for the list for a lich who knows full well it's going to have to obliterate some high-level interlopers (aka PCs).

Sorry for not being clear about that from the start.

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But why would the lich ever allow this circumstance to occur and risk losing? Why would it risk itself, why would it "fight fair?"

I said this in the other thread. Rather than a specific list of spells, the spells chose will be based on what the lich feels is best for the particular time and place of the encounter. Liches are super geniuses who have had centuries to acquire lost knowledge and magic items (that's their main goal in undeath). They have seen heroes come and go. They will most likely have seen just about everything, so they will most likely not be caught unaware of the PCs motivations and will have been prepared for them.

A lich will also use its immunities to its advantage. In the other thread, I mentioned something like having a command word trap in place to where the PCs enter the lair, it gets sealed off and then filled with water, since liches don't need to breathe. If you don't have water, use some other variant of that, maybe a vacuum that sucks out all the air. A lich will also assume that anyone with basic divination spells can find it's phylactery, so it will take measures to protect it so that even with detection spells, it will not be easy to get ahold of. That means the lich comes back to get revenge in the case it is defeated.

The first things that pop into my head are time stop and globe of invulnerability. If he knows the party is coming and has a minute to prepare, conjure elemental is decent, too (it does not require concentration). Ditto for mirror image. Concentration is actually a huge problem for the lich; if you want to cheat your head off, letting the lich concentrate on multiple spells would really amp up the danger.

[MENTION=53176]Leatherhead[/MENTION]: polymorph only allows beast forms, so it's not quite as good as being a solar or a dragon or something. I think T-Rex is the best option there, and giant gorilla is not bad. Plus, it's dispellable, so it's not quite as deadly as two-encounters-in-one. The rest of your spell picks are spot-on; wall of force is particularly nasty when used well.

With three casters in the party, I'd imagine this devolving into a counterspell showdown, so focussing on staying out of sight is pretty important. Greater invisibility is good, but simply having a lair with lots of nooks and crannies and making good use of misty step should work too.

Hmmm...

*if* for some reason the lich can't charm/force/hire someone else to do it, and if it's confident its philactery will "bring it back", a suicide mission might be a valid strategy. In this case the lich's goal would not be to destroy the entire party (it might fail) but instead insure permanent harm by focusing all its effort on killing (*permanently*) one PC, or destroying/stealing magical items.

A series of hit and run/(die and reform) attacks might make more sense than a full on direct confrontation.

A variation on this idea: A quick hit an run (not hit and die). The party is frustrated, and builds a counter plan (bonus if the lich can spy on them while they do so, it might place a magical tracker/spy/etc while it attacks). So when the lich comes back and does the same, they follow him - but the lich is leading them into a trap.

You know your players and how they would react. So does the lich

Sacrosanct said:

I said this in the other thread. Rather than a specific list of spells, the spells chose will be based on what the lich feels is best for the particular time and place of the encounter. Liches are super geniuses who have had centuries to acquire lost knowledge and magic items (that's their main goal in undeath). They have seen heroes come and go. They will most likely have seen just about everything, so they will most likely not be caught unaware of the PCs motivations and will have been prepared for them.

A lich will also use its immunities to its advantage. In the other thread, I mentioned something like having a command word trap in place to where the PCs enter the lair, it gets sealed off and then filled with water, since liches don't need to breathe. If you don't have water, use some other variant of that, maybe a vacuum that sucks out all the air...

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This is what I was getting at in my previous comment. In a prior campaign, I modified a Liche into something I called a Sea Liche (an Undead Lovecraftian Fish Person Wizard). The Sea Liche's resting place was in a temple on the back of a Leviathan. The Sea Liche could command the Leviathan to submerge, effectively drown/flooding everything.

Terrain, especially the lair, can really crank up difficulty with no changes to spells and ability.