Start Instant Action mode, choose your levels, but do not launch. Go down to the options, then go on "Hero". Change the options here as follows: Best Player, 4 Points, and the time for the hero to become available to 4 seconds. Your hero or villain can still die and the meter runs out, but you only need to kill four people for 4 points to unlock the hero or villain again. Also, if you get the points when you are playing as the hero or villain, when you die when playing as the hero or villain they still count as the points; you can pick to play as them immediately.

Go to Instant Action, select your levels, but before you start go to the options menu. Select "Hero" then change options to Best Player, Time Limit 1 second, and the time for hero to become available to "Always". You can start the game selecting the hero, and when you die you can pick them again immediately.