Power-Up is a mechanic in Skylanders: Ring of Heroes to increase a Skylander's power. Used five times per Evolution, it is a small stat increase that takes Soul Stones and Upgrade Elixirs (and at later levels, Elemental Stones), and necessary to Evolve each time.
Power-Up is identified by text from 1+ to 5+ next to the character's icon. Villains can also Power-Up and also require it to Evolve, but they take a smaller amount of Stones and Elixirs to compensate being rarer in number.