So the board is 1
Grimlock on Player 1’s side and a
Metroplex and Scamper on Player 2’s side. Player 1 attacks Metroplex since Scamper is untapped and unable to be targeted. Then Grimlock gets enough attack to kill both characters with skill since Metroplex is heavily damaged and Scamper has low defense and life. So, since the Grimlock attacked Metroplex while Scamper had
Heroism, I assume that since Heroism only changes where the damage goes and not the actual attack that the damage a character takes through the effect of Heroism is effect damage and not battle damage. I want to know the ruling because if the damage IS battle damage then Grimlock’s skill does trigger and Player 2 loses, since Scamper would die as the rollover would kill Metroplex but if it is effect damage, then Grimlock’s skill wouldn't trigger and only Scamper would be KO’d.
[Source: WotC] 
The damage redirected by
Heroism is still attack damage. So Scamper would take enough to get KO’d and then
Grimlock’s ability would trigger and the defender would have to assign the extra damage to
Metroplex.
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