Actually, I figured it out on my own. Still not sure why it was crashing, but all it took to fix it was importing him into another rig's file that was working. Yay!

Malcolm was working perfectly fine for hours while I was posing it and playing with all the controls, but the second I started touching the timeline it crashed with a "fatal error" and I can't even do basic animation. Even just clicking a new frame on the timeline crashes it.