A zero-to-death, also called zero-death or 0-death for short, is a particularly long and intricate combo that starts on an opponent at 0% damage and ends with the opponent being KO'ed. Zero-deaths are related to infinities, but are not the same. While an infinite can continue forever regardless of damage percent, a zero-death must come to an end as eventually the opponent will be knocked too far away to continue comboing if they are not finished before then. However, zero-deaths and infinites are functionally equivalent, since infinites are utilized to zero-death the opponent, with their only additional utility over zero-deaths being able to stall by continuing the infinite beyond KO percent, which all serious tournaments have a general blanket rule forbidding.
While combos of some sort are relatively common; zero-to-death combos require almost perfect timing and placement in order to properly work, and even a single missed or mistimied hitbox can ruin a combo. A zero-to-death combo was hard to pull off or impossible to perform in Super Smash Flash due to how hard it was or impossible to combo due to the high knockback that the attacks dealt and as well characters were most likely able to survive due to them being able to recover back to the stage. It is much easier, although still difficult, to perform a zero-to-death combo in Super Smash Flash 2 due to the improved physics.
Zero-to-death combos are mostly seen when chain grabbing is being used or in certain character match ups.