mtg planechase card size Oversize Sleeves 3.6 inch x 5.1 inch (91 mm x 130 mm), Fit for Plane Chase Cards, Dr. Who Commander Deck, Large Card Sleeves : Toys & Games Stairs to Infinity (Planechase Anthology)

Not only can you play a cost 6 (or less) Song for free when you play him, but he also counts as a 6 cost character for playing other Song cards too, thanks to his Singer 6 keyword

Its also easy to get it back to your hand, allowing you a chance to do it again

Doubling your mana sets up explosive turns, and you can apply pressure after with your animated Mountains

Do note that you cannot save yourself or protect yourself from colorless damage, so something like a colorless flyer such as Steel Hellkite will prove a problem, or colorless targeted removal like Scour from Existence or Karn Liberated

Who knows, maybe Mystery Booster 3 could bring both Axavar and Sliver Weftwinder into paper, if their abilities allow it