The Whisperer is a hostile mob exclusive to Minecraft Dungeons, It appears in the first dlc: Jungle Awakens.
It looks like a tree that has no face but a mouth, it also has a purple flower on the top of its head, it has a glowing gold-purple-pink exoskeleton, which means it was created from a Orb of Dominance Shard, It was also one of The Jungle Abomination's Minions, along with the Leapleaf.
This Mob can summon other entities just like The Evoker.