Reaper

Menace
{t}{b}{b}: Reaper deal combat damage to target
creature and target creature deals it's combat
damage to Reaper. If Reaper would be put into
graveyard it's toughness becomes 1 until
end of turn instead.
{x}{x}: Play this only after defenders are declared.
If 3 or more defenders are declared to defend
Reaper. Reaper gets +X/+X until end of turn.
Where X is the number of declared defenders.