Monster AI selection is an AI mechanic that responds to current combat state.
1.Response: AI decides to counter-attack, either melle or ranged attack(hit-and-run) to keep desired range.
Default attack skill is usually physical or limited to elemental projectiles.
AoE spells and offensive auras are usually attribute of boss monsters and should not be used for mundane types.

2.Skill: AI has a percentage chance to use special monster skill X when target is in range. Monsters may have multiple skills: they will choose one dependent on distance and target location, or use one randomly(with n% chance). Avoid one-hit kill skills in favor of debuffs/curses.

3.Flee:Flee after N% life loss or due target stats(levels vs monsters, buffs(e.g. fear buff)). Teleport type skills may be used to quickly increase distance if monster has them.
Many games don't implement fleeing mechanic as it makes combat longer and cumbersome, instead most monsters fight to death.

4.Defense: use defensive skills(block/on-hit skill) or attract nearby monsters(assist/call for help (in radius N, esp. flying monsters need limits)). Auras/On-hit skill/Buffs are common variants that engage on attack.

5.Idle: moves in circles around the designated spawn area.

6.Cursed: Under effect of spell/skill/aura, assumes the AI behavior required by effect/aura/spell(e.g. change in speed).