Spellcaster
Skirmisher
Displacer Beast (CR 3) Both independent and as a minion
Chasme (CR 6)
Incorporeal
Ranged
Vrock (CR 6) (Note: as one of the few monsters in D&D with ongoing damage effects, the vrock has a somewhat unique combat style)
Cyclops (CR 6) Poor aim, but deadly area effects (see article)
Ambusher
Quasit (CR 1) Also used to spy of PCs, and similar stealth tactics
Suprise Attack
Brute
Grappler
Maralith (CR 16) (More tank than grappler. Locks down PCs instead of moving them.)
Chasme (CR 6)
Reverse Grappler
Boss Monster Tactics
Lair Actions
Flyby
Unique Abilities
Heist Obstacles