In the Tomb of Annihilation adventure, one of the last encounters is against the Soulmonger, a cylindric evil artifact suspended over lava by three adamantine struts.
The artifact can defend itself through its tentacles:
Tentacles. Once per turn, in response to any creature making a successful melee weapon attack against the cylinder or one of its struts, the Soulmonger attacks that creature with one of its 30-foot-long tentacles. The tentacle bas a Strength score of 22 and makes one melee weapon attack against the creature: +7 to hit, 24 (4d8 + 6) bludgeoning damage. Instead of dealing damage, a tentacle can grapple its target (escape DC 16). If the target weighs 330 pounds or less, the tentacle can also lift the grappled creature and move it to any unoccupied space within its 30-foot reach, or drop it in the lava.
Can a tentacle grab and drop a creature into the lava during the same turn? Or is it intended two take two turns (one to grab the creature, one to drop it)?
Normally, a grappling creature could grab a character, drag them somewhere, and drop them all in one turn, but I'm unsure how the tentacle are supposed to behave.
Note that the PCs could be level 11 at this point, so a drop into the lava is unlikely to kill a melee character outright.