Helly everyone,

I am looking for an encounter idea for my group of 4 third-level players. Tharizdun, the chained oblivion leaks some of his black mass through the surface and starts to infect or summon some lesser threats that the players may be able to kill.

Any ideas on which monsters fit or which monsters to choose?

Thank you a lot in advance!

A star spawn mangler or wraith (a piece of Tharizdun's essence) could be a challenging final boss encounter if they're fighting a cult of Tharizdun. Smaller fights that lead up to that could include a cult fanatic (with the Tharizdun's Spark trait), a star spawn grue and two cultists; three cultists and a nothic or gibbering mouther; and a madcap.

One of my favorite monsters that's really dark and messed up but still more or less appropriate for that level of player is a Dybbuk. It's a CR4 creature, so a single one makes a solid challenge for a level 3 party. It's basically a Deadite from the Evil Dead series... a sort of incorporeal spirit that possesses dead bodies, twisting and manipulating them, causing the bodies to move something so unnatural and unnerving it actually calls for a Wisdom Saving Throw to avoid the Frightened Condition.

Works best in a situation with multiple bodies in one room. Maybe a cult sacrifice or maybe the burst of black mass that initially triggers the event just straight up kills a group of merchants or something, then the bodies start getting up and killing people.

Ghouls reskinned as people with pale, ashen skin and and milky white eyes with black, inky slime leaking out out their eye sockets, they moan maddening whispers of a giant who, in his pursuit of power, turned the to eldritch Magicks of a plane beyond understanding, the gods, disgusted by his blasphemy of reality as we know it, chained him inside the earth to forever be trapped underneath the ground that men tread.