Idea: "support entities"
There can only be one support entity per round, and they cannot spawn if there is only one entity that spawns on the map.
First one: "idol" basically how it is in ultralkill, picks the strongest entity on the map, and makes it invincible. But if you walk up to it and hold the interact button for 3 seconds, you break it. Causing a loud noise that attracts monsters, and despawns it for 25 seconds.
Second one: "flesh" (part of the nullscape colab)
Deals heavy tick damage, about the same as telefragger, also Slowly wanders the map, infecting the floor beneath it. Stepping on an infected floor causes prisoners to be slowed down, and entities to be sped up. It also "infects" players, causing them to leave behind a smaller, but just as potent infected trail. But after 7 seconds of being infected you become immune for 15 seconds. Infected players can be identified by the giant eyeball on their head.
"Medi-bot" wanders the map, in search of an entity. Once it finds one it will trail behind it at its running speed and will give two random buffs. Buffs include: increased speed, decreased stun duration, increased I frames, increased damage, bleed/extended bleed duration fire/extended fire duration. If it encounters a stronger entity it will abandon the current one in favor of the stronger one. But the medi-bot suffers from 2x stun duration. But it has double the I frames too, and also when exiting its stunned form it rerolls its effects.