You may have Gigantoplasm enter the battlefield as a copy of any creature on the battlefield, except it has ": This creature has base power and toughness X/X."

Devour 3 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters the battlefield with three times that many +1/+1 counters on it.)

When Ravenous Gigantotherium enters the battlefield, it deals X damage divided as you choose among up to X target creatures, where X is its power. Each of those creatures deals damage equal to its power to Ravenous Gigantotherium.