As Wood Elemental enters the battlefield, sacrifice any number of untapped Forests.
Wood Elemental's power and toughness are each equal to the number of Forests sacrificed as it entered the battlefield.
Tap an untapped Zombie you control: Target land becomes a Swamp until end of turn.
Tap an untapped Zombie you control: Target creature gains swampwalk until end of turn. (It can't be blocked as long as defending player controls a Swamp.)