With some more work, you can really make this something great.
I found a couple bugs.
1. (which I tried to reproduce but had a hard time with it) On the first turn, I waited until the timer went to 0-5 and shot an grenade. The game said player twos time was up, and player 1 had a turn again.
2. This works for either turn. When the timer is almost up, if a grenade is thrown by for example player 1, and player 2 walks into it, it is no longer player 2's turn.
Perhaps you want to use a clamp for when the player launches their grenade, and keep the -0 from going below 0. Also, make a wait time, so the next player can't have their turn until the last players grenade has been blown up.
All in all, its fun and well designed. Not sure if anyone else has experience this but the sprites aren't either overlayed or have no alpha channels.
1 I saw and did correct I believe in the two separate downloads , when I worked on the turn timer
I forgot that I also switched turns when the grenades exploded , so I simply changed that so it just timed out the turn timer and let the turn timer handle the turns .
the third one I have not experienced except when
changing resolution or tabbing out as Kartoffel said , I did not plan for different resolutions .
However I cannot explain why it blacks out , maby its due to locking the bitmaps frequently and blitting .
edit : okay I just saw it too on timer 0 , probably a wait error , I think the timer switches before the wait in check players return with a switch or something , hope I am allowed to update if I correct it
