This is a Paper Mario game. The rules are simple: Mario will choose a random attack (Jump, Hammer, Blazehammer, Hopslipper, Heal). You wouldn't need to time those attacks; it's based on luck. When it's Bowser's turn, he'll choose a random attack. But don't just wait and have Mario get attacked. Press A on your keyboard to decrease damage at the right timing when it's Bowser's turn. (Remember, don't mash the A button when blocking. There's always a cooldown (of 0.5 seconds) before you can block again)
Thanks to @Superkoopa_64 for the original project Paper Mario Color Splash for the Mario sprites and some of the sounds.