Arboreal Grazer is also a popular ramp card that costs only 1 mana, but the nice thing about Growth Spiral is that at the very least it does replace itself in the late game where you probably have a ton of additional mana anyway while Grazer does basically nothing
But what really makes Hullbreaker Horror so good is how it combos with so many cards to enable some truly silly things
Nissa, Worldsoul Speaker Nissa, Worldsoul Speaker is a fine energy payoffcasting spells for any resource other than mana is inherently broken, after allbut I like it best as an energy generator
6 Kraum, Ludevic's Opus The blue part of the Blue Farm cEDH list, Kraum, Ludevc's Opus often comes together with Tymna the Weaver to make one of the best decks in the format
He worked a lot differently back in the day before the rules changes, but he is still just as strong (some might even argue stronger!)
How many sources of card advantage in a Commander deck