An idea a player of mine is having to use an ability in a video game in a prestige class, but we're having trouble transfering it into the D20 mechanics. In Shinobi 3, the character sacrifices his life (losing his life, but in a video game you have 4 of 5 lives) and all the opponents on the screen die. My idea is that the PC would, as a full-round action, magically forfeit his life force (drop to 0 or -1 hp) and all those within a 30-foot radius would have to make a Fortitude saving throw (I'm thinking against a DC 10 + caster level + constitution modifier) or die. I think that's reasonable. He doesn't like the fact that we don't know of any other thing in D&D where you forfeit hit points or ability points for an effect.
Can anyone give me a recommendation on what to do or an example of forfeiting HP for an effect?