Power-Up is a, well, powered-up version of Kicker, where an incoming creature can gain powerful extra effects for an extra cost
This can be before blockers are declared, after blockers are declared but before combat damage is dealt, during combat after combat damage is dealt, during the postcombat main phase, during the end step, or, in some unusual cases, during the cleanup step
You have better options once you branch out to multicolor decks, but this looks right at home in casual mono-white equipment lists
Potentially prophetic rival name aside (given the prevalence of Pokemon TCG in McDonalds Happy Meals), the game is able to offer an entertaining, and more cost-effective, way of playing the TCG, even if it cant quite beat the rush of opening a pack in real life
it essentially doubled the Game Boys life span