custom backup mode:

Allows you to choose what npcs come out of the portal, for example: letting headcrab zombies spawn in fast zombies or poison zombies would be cool

and it would be funny seeing smth like a headcrab summon a ant lion lol

2nd suggestion: team mode
ties into the first suggestion, any faction that comes out of the portal is automatically not agro example: headcrab and antlion would be friendly

these would be cool ideas