Reliquary Tower isn't terribly common in Modern, so I don't know if it's too much of a concern. Some Gitaxian Probe might not be a bad idea to thin the deck and get you to your combos faster. Possibly Serum Visions, not that you really need the draw, but it's probably the best card in modern for digging to get the cards you need. I like what you're doing here.

Thank you. And I'm not sure what I'd replace if I put those cards in... The deck is in a fragile state right now; it works the way it is, and it's really easy to mess it up by changing one or two cards. Do you know of anything I could safely replace?

Well, my first thought is Birds of Paradise, because they aren't benefiting from Heartbeat of Spring, and you have to cast them with a green mana in order to get blue from them (and you are running more islands than forests here).

Removing them would require a bit more mana fixing in the way of lands. I don't know what your budget for the deck is, but Flooded Grove would be sick with Heartbeat of Spring, letting you potentially tap for 9 mana on turn 4. I realize, though, that this would add a good $80 to the price of your deck, and part of its appeal is that it relatively budget-friendly.

Just my thoughts. You have actually played with the deck. Are the birds really helping you that much?

They let me use Heartbeat of Spring a turn earlier than usual. It makes it instead of turn1, land, turn2, land, turn3, land, Heartbeat of Spring, it's turn1, land, birds, turn2 Heartbeat. The main appeal of the card was originally so that I'd have something to play on turn 1. So I may try replacing it with Serum Visions and see if it still functions, I guess.

But I'm doing that tomorrow. I have Thanksgiving to get to right now.

On the Birds of Paradise question, you could try Arbor Elf instead, which would get the benefit of Heartbeat of Spring but would only be able to produce blue mana if you have a Breeding Pool on the field.

Yeah. I have thought about running Arbor Elf instead. I've also considered running Overgrowth with it. I probably won't be able to fit both, though. I'll try the idea and see if it works as well.