Velis, Life's Climax

{4}{b}{r}{g}, {t}, Pay X life: For each number that
isn't part of a cost on target creature card with
converted mana cost X or less, double it until
end of turn. That creature attacks this turn if
able, and you and its controller may activate
each of its activated abilities once this turn
without paying their costs. At the beginning of
the next end step, its controller sacrifices it and
loses life equal to its power. (Double the values
of X and * as well.)