Boss Encounter 12 - lvl 5 to 10

1x Blight Lich Medium undead , any evil alignment
Armor Class 17 Natural Armor Hit Points (15d8 + 72) Speed 40 ft.
STR 18 (+4) DEX 16 (+3) CON 18 (+4) INT 18 (+4) WIS 14 (+2) CHA 16 (+3)
Saving Throws DEX +7, CON +8, WIS +6, CHA +7 Damage Resistances Cold, Lightning, Necrotic Damage Immunities Poison; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks Condition Immunities Charmed, Exhaustion, Frightened, Paralyzed, Poisoned Senses Truesight 150 ft, Passive Perception 12 Languages Common and any 5 languages common and any 5 other languages Challenge 12 (8,400 XP) Proficiency Bonus +4
Spellcasting. Cantrip: Mage Hand, Prestidigitation, Shocking grasp, Warners' Worthless Whispers
1st level (4 slots): Detect Magic, Magic Missile, Shield
2nd level (3 slots): Detect Thoughts, Mirror Image, Misty Step, Acid Arrow
3rd Level (3 slots): Counterspell, Counterscry, Fly, Animate Dead, Dispel Magic
4th Level (3 slots): Banishment, Blight
5th Level (3 slots): Scrying, Wall of Force
Actions Multiattack. The Blight Lich Makes two attacks: two with the Blight Staff. it can use Pestilence Push or Decay Clutch in place of any melee attack.
Blight Staff. Melee weapon attack: +8 to hit, Reach 5 ft., one target. Hit: (1D8) slashing damage plus (2D6) poison damage. The target must make a DC11 Constitution saving throw, taking the full poison damage on a failed save, or half as much of damage on a successful one.
Pestilence Push. Ranged Spell Attack: +10 to hit, reach 150ft., One target. Hit: (4D6) poison damage. On a successful hit 18 or higher, the creature is pushed back 5ft. in a single direction.
Decay Clutch. Melee Spell Attack: +8 to hit, reach 5ft., one target. Hit: (1D8) Poison damage and it cant take reactions until its next turn.
Reactions Turn Resistance. This creature has advantage against any saving throw against any effect that would turn undead.
Legendary Actions Legendary Resistance (1/Day) If this creature fails a saving throw, it can chose to succeed instead.