Custom critical strike

[Boneslasher]

Could someone make a custom critical strike-like ability? it must be an ability which can be activated by a button (like a non-passive ability) and must inflict 3/4/5 times normal damage at level 1/2/3
and must have a mana cost of 75

Do not care for the icon and the position in the command card. Ill fix them myself!
PS in order to make the ability recognizable, please call it Killing Strike or somethig like that

THX!!