Nope. As far as I know, no playable demo exists. I made a bunch of graphics after we finished Bombaman XXXtra ammo but more than an editor was never made. I don't even have these graphics anymore and everyone moved on so I don't think that Blox will ever be finished.
I don't know why the mouse routine isn't working (it was made by msd so I guess it should work ) but without mouse it's possible to play the game. The screen is messed up though: Looks like interlacing is still enabled even though the function.
Ok there seems to be some errors due to sjasmplus being incompatible with sjasm, and I can't assemble the thing with the latest sjasm version...