Riken, Gluttonous Goliath

When Riken enters the battlefield, sacrifice all
other creatures you control. Riken perpetually
gains all abilities of all creatures sacrificed this
way. Put a +1/+1 counter on Riken for each
creature sacrificed this way.
With insatiable hunger, Riken devours the life force of
all who stand before it. Each feast bestows upon it the
prowess of fallen champions, a grotesque
amalgamation of power and ambition.