The thing holding it back is simply that it is pretty fair compared to the other stuff the deck can play, especially at the 3 mana slot
Youre much better off protecting yourself with a pillow fort card, like Ghostly Prison, and letting Smashy Gruul Man work for you instead of muzzling him and getting bitten three turns later when this useless Aura is inevitably removed instead of the combo players Rhystic Study
Anyway, back on topic, all Ramp decks since the beginning have looked to build their mana to ridiculous levels as quickly as possible and then use that advantage to drop more powerful win conditions earlier than their opponent and ride that to victory
Triggered abilities of colorless spells
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Information about the M Kangaskhan EX XY Flashfire Pokmon card : This card was released in 2014