So does giving this card Flash suddenly make it a bunch better? Interestingly enough, this card works best with Kruphix, God of Horizons, and not Karametra, God of Harvests. Since the effect works for all players, Kruphix’s ability to turn any excess mana into colorless mana is really good. Five mana is a bit much for an enchantment like this, though, but more stomach-able if you’re playing a Kruphix deck in which you’re really only paying 2 Green for it. That’s something I’m sure R&D took into consideration. Heartbeat of Spring now would be a staple in that kind of deck (hello, Modern potential).
It’s probably going to see a little play in a Kruphix type deck, but that deck is already full of five-drops. It’s going to see some Commander play, certainly, especially alongside Kruphix, for a bit extra redundancy along with the cards mentioned earlier, as this effect does stack upon multiple instances. It’s definitely a usable enchantment, and used correctly the Flash can help you take advantage of it first. It’s okay.