Champion

• 20% chance of being chosen when a random Champion or Unique pack spawns. Champions also spawn from Evil Urns in Act 5 and Monster Shrines throughout the game, and in some set locations:
  • Tristram
  • Crystalline Passage (guarding entrance to Frozen River)
  • Glacial Trail (guarding entrance to Drifter Cavern)
  • Drifter Cavern
  • Halls of Vaught (end of hall)
  • Frozen Tundra (guarding entrance to Ancients' Way)
  • Ancients' Way (guarding entrance to Icy Cellar)
  • Icy Cellar [1]
• Spawn in groups of 2-4: all but one are always Champion, with the remaining having an equal chance of being Champion, Berserker, Fanatic, Ghostly or Possessed. [2]
• If the following spawn as Champions, any minions receive the life and level bonuses of Unique minions:
  • Fallen
  • Fallen Shaman
  • Scarab Demon
  • Fetish
  • Blow Pipe Fetish
  • Fetish Shaman
  • Siege Beast
  • Overseer
• For all Champion types except Berserkers, level is normally monster level +2: this level is used for chance-to-hit, aura and curse level calculation, selecting relevant MonLvl values to calculate base attack rating and damage of all types, and the clvl/mlvl modifier applied to experience when clvl < mlvl; base level continues to be used to calculate base defense, life and experience. [3] [4]
• Ignore Target's Defense does not apply but -% Target Defense from items is 100% effective.
• Freeze length chills instead; only minions can be frozen.
• Stun length only has 10% chance of being applied, but suffers no other penalty.
• Effects altering AI cannot be applied directly.
• +% Damage from Champion bonuses is halved then rounded down when applied to Willowisp Champion melee physical damage due to a now undocumented change in 1.13. [5] [6] [7]
• Life drained by Open Wounds is halved.

Stat	Normal	Nightmare	Hell
% Base Life	300	250	200
% Base Experience	300	300	300
+% Attack Rating	67	56	49
+% Damage	90	75	66

• +20% movement speed [8] [9]

Reference

• 1.13 LIVE -- LADDER RESET (General Diablo II Discussion)
• 1.13b PTR is Live (General Diablo II Discussion)
• Patch 1.13 Realm is alive (Technical Discussion)
• Special Monster Bonuses (Arreat Summit)
• Nefarius, Boss Status Modifications (1.11b) (Phrozen Keep)
• Onderduiker, Monster Bonuses, Death Damage and Corpse Explosion (Technical Discussion)