When I played last year, the answer was “none”. So far as I can tell, that is still the case, since it looks like only Wizard skills are available, along with other Runecaster skills.
none. no fun allowed.
After wizard rebalance, fireball stays for 10 seconds after exploding, and Pyro c2 has an attribute to increase the duration for +5 seconds too. I’m pretty sure the combo still works after the fireball explodes and stays on the field, but I’m not 100% sure