Looking to spice up the final encounter

Hello everyone seeking ideas for a final crescendo of a combat I was originally just going to do a death knight and a couple of skeletons for a 7 player one shot, but since this was for most their first time I wanted them to do things in a bang, as I was thinking of doing a zombie horde, have a mass amount of zombies, all 1 hp or so, and have then swarm the party but have then weak so they don’t wipe them, still having the death knight but be a force controlling then until the numbers are low, then he’ll join the fray, any ideas would be appreciated to hopefully balance it out or, especially any puzzles or traps will definitely be appreciated!!!