Hydra Broodmaster

2014-04-26 An ability that triggers when a creature becomes monstrous won't trigger if that creature isn't on the battlefield when its monstrosity ability resolves.
2014-04-26 Monstrous isn't an ability that a creature has. It's just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.
2014-04-26 Once a creature becomes monstrous, it can't become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
2014-04-26 The value of each X in Hydra Broodmaster's last ability is equal to the value chosen for X when its monstrosity ability was activated.

Card is in preconstructed decks:

mtg.wtf