Improv is all about the element of surprise, and these two sure-to-sell-out shows have more curve balls than a little league game. That’s because you never know who’ll show up on stage. Of course, there are the usual suspects, the Theatre 99 regulars who perform on that stage several nights a week. But then there are the wild cards, the out-of-town comics who head to the theater after their own shows to jam with their festival hosts. And while most improv groups have a chemistry borne from months or even years of working together, the folks on stage at these events may have never even met. Friday’s JAM will be strictly improv, and at $5, it’s one of the best bargains of the festival. Saturday night is more of a grab bag, with improv, sketch, and stand-up from a bunch of festival artists. —Erica Jackson Curran

All Star JAM. Fri. Jan. 18, 11 p.m. $5. Theatre 99.

Festival Finale. Sat. Jan. 19, 10:30 p.m. $18. Theatre 99