There is a cheat in the melee section of SC3. Pressing ALT-F9 during a battle starts it over from the beginning, restoring the health of you AND your enemy and removing the planet (if there was one) in the process. There is a bug in SC3 that is to your advantage, kill an enemy and hit
ALT-F9 while he's exploding.
The battle will restart, your health and YOURS ONLY will be filled back up, and your enemy will die immediately.
Various Cheats
Enter any of the following keys during gameplay to activate the desired effect.