Summary:
Mob twitches and emits black particles when killed with a totem in hand via the /kill command. This applies to all mobs. Also, this behavior of mobs is not in version 1.18.12.

Steps to reproduce:

1. Summon any mob.
2. Give the mob a totem of immortality (you can use the command /replaceitem entity @e slot.weapon.offhand 1 totem_of_undying)
3. Write the /kill command.

Observed results:
Mob twitches and emits black particles (similar to potions).

Expected results:
Mob will simply die without twitching and with emitting white particles on death (as in 1.18.12).

Image: