Self Control is a buff that that helps avoiding negative effects (debuffs) being cast on the hero.
While in the battle, you can tap and hold the Buff icon and read what it does.
It's mostly known to Panda heroes, but some others as well, here is a full list:
  • Rin the Unseen (Ability 3)
  • Patriarch Qi (Ability 3)
  • Kin Li (Ability 3)
  • Shao Lin (Ability 2)
  • Kang Xi (Passive Ability)
  • Lei Zi (Ability 3)
  • Kulai ( Ability 2)