If you cast a spell for another cost "rather than pay" its mana cost, you can't choose to cast it for any other alternative cost
Number 7 Language English Legal Formats Brawl, Commander, Competitive Brawl, Historic, Legacy, Modern, Timeless, Vintage Not Legal Formats Alchemy, Pauper, Pioneer, Standard Rulings (3/16/2018) A mana cost of means that you pay twice X
Its also indestructible, so its tougher to deal with outside of exiling effects typically in white
I hesitate to call Aurora Phoenix a powerhouse card, and if anything Im learning that phoenix creatures arent really at their best in Commander
Moat, on the other hand, Moat asks nothing of you
Still, with that said, I love this game above all others for a single, indisputable reason and that is that it captures Middle Earth with such perfection, such epic scale and so much thematic joy through its gameplay and art that I honestly could not bare to ever put any CCG above this one