One of our heroes has the knockback ability (skill card I think). If another hero gets grappled, can the hero with the knockback free the grappled hero by knocking him away from the monster? I assume so, since the grappled hero isn't spending any movement points, but thought I'd make sure.

Can a hero use knockback on himself? I assume not because I don't think you're allowed to attack yourself, but what if under Dark Charm and ordered to attack yourself? Though in that case the overlord gets to pick where you're knocked to.

Yes, a grappled hero can Knockbacked (or is it Knockedback?), just like any other figure.

No, a hero cannot attack himself unless under a Dark Charm or Animate Weapon (or using Blast, but this doesn´t come with Knockback), and in that case the OL will decide whether and how to use the Knockback.

Thanks. That's what I thought, nice to have it confirmed.

Though it'd be funny if the grappler could choose to keep his hold and thus be knockbacked with the hero

Do note, however, that if one hero uses a Knockback attack to free another, grappled, hero, he must apply the entire attack roll. The attacking hero can minimize damage output by not spending surges and choosing +1 range instead of +1 damage on power enhancements, but if the base roll is enough to hurt the target hero, the attacker cannot "choose" to waive the damage dealt.