CW: Body horror
So, id like for you to imagine, a magical scroll, maybe they find it in a lich's old lair, an evil spell
"When you cast this spell, you may choose a creature you can see, they then must roll an intelligence check or be cast away to find a horrible death and be sent to the tom
It can be cast once per day & recharges whenever midnight hits"
This is a once per day practical banishment spell right, It's intentionally balanced by the roll to give a false sense of security to the players
Keep a tally on every creature the group banishes
But theres a secret cypher written on the bag of the scroll, now your players could try and solve it, in which case theyd find out the true nature of the scroll, but lets say they dont coz, free banishment
Whenever you feel like it, set up a quest, could be retrieving a powerful magic item, a rescue mission, smth important or personal
When they arrive, they inmidietly recognise the place, they have made their way onto the tomb of horrors
But its different, it seems that the legends were true, a party once came and ransacked the place already
All the traps are triggered or dismantled, the magical aura is all but a fading remnant of this place's architecture, the walls creak and groan. Seemingly struggling to keep themselves up
When they venture into the deep dark tomb, the scent of miasma starts to seep in, through some checks perhaps, the entrance behind them shuts
They venture deeper and deeper, the tomb seemingly expanding beyond normal means
It is then that they hear squelching creaking & groaning
Something shifts beneath them, something big
The floor collapses, as they are in a large dark chamber, face to face with it
An amalgamation of every creature, person and monster they ever banished, molten and fused together
Maybe the reveal only comes as they start to recognise pieces of it
A pile of flesh, fur, oozing fluids and metal bent & torn, groaning in agony
This is what the cypher mentioned: "Grant thee, an audience with the olden lord Acererack, pity thy flesh, thy soul to him, give yourself entirely, eternally"
& yeah for stats, its a blob, so you can take the max health of everything they ever banished, add it up and multiply it by 1.5
It cant attack so, just gotta roll strength or dex saves to not be consumed into the pile
Anyway! Hope youre having a good day :3