Worldheart Phoenix
Creature — Phoenix
Flying
You may cast this card from your graveyard by paying 
rather than paying its mana cost. If you do, it enters with two +1/+1 counters on it.
Aleksi Briclot
Modern Masters 2015 (MM2)
• #135Rulings
As soon as you start to cast Worldheart Phoenix from your graveyard, the card moves onto the stack. At that point, it's too late for an opponent to prevent you from casting it by removing it from your graveyard.
(wotc • 2009-02-01)
If you cast Worldheart Phoenix this way, it is a spell and can be countered.
(wotc • 2009-02-01)
Casting Worldheart Phoenix from your graveyard by paying its alternative cost doesn't change when you can cast it. You can cast it only at the normal time you could cast a creature spell.
(wotc • 2009-02-01)
Rulings
As soon as you start to cast Worldheart Phoenix from your graveyard, the card moves onto the stack. At that point, it's too late for an opponent to prevent you from casting it by removing it from your graveyard.
(wotc • 2009-02-01)
If you cast Worldheart Phoenix this way, it is a spell and can be countered.
(wotc • 2009-02-01)
Casting Worldheart Phoenix from your graveyard by paying its alternative cost doesn't change when you can cast it. You can cast it only at the normal time you could cast a creature spell.
(wotc • 2009-02-01)