Welp, the author already broke his setting. It was specifically said that unlike the hero he'll have human limits. So immediately giving him a limit removal defeats the whole point of him needing to be an assassin. The hyper regeneration also doesn't make sense given the level the hero is supposed to be. If you ever take damage from that kind of hero you're going to die, either immediately from a one hit K.O or you'll no longer be able to escape anyway and still die.
The one choice I agree with is the chant weaving but they should have just made that spell weaving, because you can't be chanting anywhere near the all-powerful hero. The versatility though would allow him to come up with unique spells that could slip through or around the Hero's defences and senses for an assassination attempt.