When I saw Leyline of the Guildpact, my first thought was, "Huh. That's weird." Second thought: "Wait, that fills all the Coalition Victory requirements on turn 0!" So, after doing absolutely no research on what everyone else was doing with this combo, I jumped headfirst into brewing.
Leyline of the Guildpact makes this deck run. It sets up a Bloom Tender on turn 2 into Coalition Victory on turn 3. It dumps out a full power Scion of Draco on turn 2, attacking if you got Mass Hysteria turn 1. ("4/4 hasty flying vigilant hexproof lifelinking first striking trampler" is so much fun to say.) It exiles almost anything with Leyline Binding on turn 1 (plus it gets that Leyline theme going--style points count!)
Unfortunately, it's also very reliant on starting with LlotGp. As it stands now, if Leyline of the Guildpact starts the game, it goldfishes a turn 4 win reliably, but it can take two or three mulligans to find one. Without it, the deck is much less threatening (Scion of Draco -> Chardalyn Dragon, Territorial Kavu -> slightly better Volatile Wanderglyph), and there's pretty much no redundancy. The Serum Powders provide a buffer against this sort of non-game. Basically, this isn't a deck, it's a Leyline of the Guildpact with extra utility.
Since LlotGp is so critical anyway, I plan to keep the basic lands here. They can tap for any color, and it saves a few life from shocklands and fetchlands, not to mention keeping the budget low and getting some more style points. When was the last time you saw a 3-5 color Modern deck with a basic land base?
Fastest potential win (two turns, seven total cards):
The sideboard leans more toward a Zoo deck build. It can fully replace the Coalition Victory + Bloom Tender set, or just sprinkle in more protection, removal, or aggression as needed. Nothing's set in stone, it's simply an idea I had. Work in progress there.
As always, thoughts, suggestions, ideas, and random musings are welcome.