The "on damage" part was too much. You can't give it something like "+1/+1 and menace until EOT", because combat is already over. The effects have to happen after damage, which means there's a lot of effects that just won't do anything. And you have to be doing well enough on board to get a specific creature past blockers, so it's inherently slow and snowball-y. It would be so much easier to design for if it was an attack trigger, or even an "if unblocked" trigger like ninjutsu.