Well, you know how to create mobs and setup a combat scenario, so the only thing you need is a list and two or three random elements from it:
rand_mobs = ["Goblin", "Giraffe", "Slimeball"]
enemy_team = Team(name="Enemy Team")
for i in range(randint(1, 2)):
mob = build_mob(id=choice(rand_mobs), level=randint(50, 55))
mob.controller = BE_AI(mob)
enemy_team.add(mob)
Something like this should work...