Toggle/hold would be best, but another interesting but simple solution would be while active you get the dmg buff by default, but get the dmg reduction half of the ability while sliding, rolling, or bullet jumping. My reasoning is that it would cause players to react to sources of big enemy damage (bombard rockets, eximus attacks, ect) with movement instead of dmg reduction just being a passive thing in the background, which sounds way more fun, and you could even make an argument for it being thematic because mirage is supposed to more acrobatic, if the prime trailer and passive are anything to go off of.