Why not have a Convention Building Be a rare spawn when Joke Monsters are on, and any zombie that static spawns in it, have those flavor items.
Maybe Even have a One of a kind joke monster inside that drops rare flavor Cosmetics you can’t find any other way.
I got 2 ideas related to joke monsters.
Second Phase to Shia LaBeouf, after you kill him the first time, he quickly reanimates once after about 5 turns. With the Message. “WAIT HE ISN’T DEAD! SHIA SURPRISE!”
Basements have a Extremely Rare Chance to have 1-3 R.O.U.S (Rodents of Unusual Size) Spawn in them.