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TW: Murder, Suicide, Influenced killing
So bloodlust in the Life Series is quite common and wellknown with the premise basically being that red-lives are splashed with this effect of a murderous rage to murder those around them. Regardless of their allies or opponments/rivals.
My headcannon or idea is that the only moment when Grian was enveloped or persuaded by bloodlust was during the final fight in 3rd Life. From the POV of Scar during the events of 3rd Life, it's inferred that bloodlust are more instinctual and a force of encourgement and the "kills" Grian committed, were more of an assistance and allyship to Scar.
Going more headcannon-omy, Grian's final fight against Scar had him receive an altered bloodlust as a final gift from the Watchers during that Life game. This kinda of bloodlust that would have Grian have tunnel vision onto escaping no matter how the deed is executed. In turn, killing his partner or ally, Scar, in his rampage for freedom but would end up trapping him. Until he ended his life to end his torment but also restart the cycle of the Life Games.
So basically Grian's only instance of bloodlust was during the final duel in 3rd Life against Scar where it was placed upon him by the Watchers as a final gift or punishment. That would result in him killing his ally.
:P that all for now.