THANKS Smiling Spectre
! 
True! (although I'm clueless what the square key is).
What puzzles me is what is the Magic key for the 2nd player.
When I'm running the DOS port (at DOSBox or DOSEmu) the 2nd player activates magic when the right key is pressed (although the same key moves the 1st player).
Seems to be a bug to me.
The 1 player mode seems to work flawlessly.
Anyway! I tried also the MAME port and the 2 players mode works as expected.