Every character has a second ability that unlocks at level 11. Abilities then either unlock or become more powerful every 20 levels, starting from level 21 and up to level 240.
The strength of these abilities increases as you level up the character. The precise level at which these abilities strengthen depends whether it's the activated or reactive ability, as well as the tier of the character.
Level 240 is currently the maximum character level that affects the character abilities.