hi i skilled golemancy and fungal arts and sometimes i can get the mustache spirit AND the slime hearder at the same time and sometimes one is replaced with the other so that i can only have 1 pet. i dunno how i got 2 pets there. i think there is a bug with summon creatures
I believe there is supposed to be a max of one summon at a time. There are bugs that allow multiples, though.
AFAIK, if you level up while having a pet, you can summon another one; and if it gets "permastunned" you can summon another one too. So, for max game breaking, try to have a pet when leveling up, summon another, permastun it, and then summon a third time. Tell us if it works!