I just tried plee-the-bear and worked my way through the training
level. All in all the game worked as expected (sometimes the jump
sequence seems stuck, i.e. although I left the space bar, plee keeps
jumping until e.g. I hit a upward wall), but after I got the fire
magic (and I might have died trying it out) the graphics vanished. The
music kept running (and also sound effects) but without graphics I had
no idea what to do.

I finally killed the game from the command line.