Can't be challenged except by a character that also has Evasive. The most common keyword in the game.
Official rule 8.6 (Comprehensive Rules 2.2.0). This keyword appears on 143 cards: 143 Character. By ink: 49 Amethyst, 49 Emerald, 45 Ruby, 5 Steel, 5 Amber, 4 Sapphire.