A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.
01-10-2007
wotc
The value of X is determined when the ability resolves. It won’t change later, even if the number of Elves you control changes.
01-10-2007
wotc
If you control no Elves when the ability resolves, the Forest will become a 0/0 creature and be put into the graveyard. However, since Elvish Branchbender is itself an Elf, the Forest will usually be at least a 1/1.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.