>>97353633
really depends on the party
a level 5 cleric would shitter shatter (most of) the fight with one spirit guardians spell

>>97353633
in theory this should be a match for four level 10s based on the CR
in practice one fireball will nuke both ghouls and all four zombies, so by turn 2 its just the ghost and the mimics (unless you play into the regeneration i guess but even then sickening radiance is on the cards)
ghosts are crazy dangerous, but they can only do so much attribute damage per turn and you have five people to spread the strain

so if you have fireball or sickening radiance prepped, and you have a frontline with respectable CON this will be safely winnable. if you have a bunch of jank multiclasses or shitters who dont contribute to combat then this will probably get at least one of them killed
basically you'll know how it's going to go by the end of round 1

>>97353633
Someone might die. Depends on how many resources they have going into the fight. Zombies are very swingy, if the party has plenty of radiant damage they’re pushovers but if they get a bunch of saves I’ve seen a single zombie tpk an entire level 1 party.

>>97353633
If you want to make it less deadly have some of the enemies enter a round or two later or the mimic not do anything until it’s “triggered”

>>97354073
Or have the encounter begin with the Mimics already in combat with the Undead. If the party start off very well, everyone remaining goes against them instead; if they perform poorly then they have Mimic ally until all the dead are down.