9. Master Ball - Pokemon
Of all the random challengers, gym battles, and Elite Four gauntlets, the simple act of catching the titular "pocket monsters" is arguably the hardest part of Pokemon.
Even the weakest Pidgey can be a handful when bad RNG lets it continue to resist getting caught, not to mention the many legendary monsters that are designed to easily avoid even the most expensive pokeballs.
That is, unless you have the Master Ball.
A staple of the series, the Master Ball is a unique, experimental Poke Ball that allows its user to automatically capture any Pokemon, regardless of how many resistances it has and how many sassy fits it throws.
The Master Ball obviously works best against legendary Pokemon, and since you get only one per game, you might want to save it up for capturing the toughest creatures.
However, if you think your level 5 Magikarp deserves a better dwelling than a regular Poke Ball, no one's really going to judge you. Just remember the choice you made when Mewtwo or Arcticuno dodged the fiftieth and final pokeball in your inventory.