This very last moment near-impossible achievement is called pixel-perfect jump. (credit to "poor kay" for reminding the term pixel-perfect).
If the player has found your secret chamber, battled past the extra-tough ninja zombies and made the pixel-perfect jump over a robo-piranha-infested lava lake, then reward him with something worthwhile or he may feel that the game is gratuitously challenging.
[Game Design: Principles, Practice, and Techniques by By Jim Thompson, Barnaby Berbank-Green, Nic Cusworth]
pixel-perfect: (video games) Involving precision at the pixel level. [Wiktionary]
Another related term is Eleventh Hour Superpower. However, this term is usually used for the final power-up right before the end of the game, usually before the final boss battle.
Many times, right as The Hero is facing his Darkest Hour before The Climax and final battle, he's rewarded one final gift from fate that gives him the strength to see his quest through.
Note that where Video Games are concerned, if the superpower is a new gameplay ability or Power-Up for the character acquiring it, it is often Purposefully Overpowered (i.e. if the player could acquire it earlier, it might prove a Game Breaker) — but the game may also regulate or limit its usage to ensure that the player can only use it at its designated time.