The key combo here is Hydra Broodmaster
+
Karametra's Acolyte
+
Singing Bell Strike
, and a devotion of at least 7. Since the Acolyte taps for 7 or more mana, and Singing Bell Strike lets it untap for 6, you effectively have infinite mana: which we promptly dump into the Hydra Broodmaster's monstrous ability to make as many hydras in whatever size we damn well please.
...Getting three speficic cards, and holding them for more than a turn or two, is a lot harder than it sounds though. For that, enter... Yisan, the Wanderer Bard! Turns out he is exactly what we need to get the ball rolling, as long as he doesn't get removed. We have Stubborn Denial and Dissolve to help him stay alive a little longer, and Kiora's Follower
+
Yisan, the Wanderer Bard
to get him playing faster (Once they both overcome their summoning sickness, and assuming you have enough mana, you can pull stuff out two at a time.) Considering Prophet of Kruphix to help this along even further, since that way we can do it on the opponent's end step as well.
Now, obviously the opponent is going to be doing their thing while we're ramping. So, we have lots of Life Gain lands (12 of them!) and Nyx-Fleece Ram to give us a healthy supply of life. Heliod's Pilgrim is there to tutor out a Bell Strike through Yisan; or, alternatively, a
Spectra Ward
to help keep our bard buddy safe. Arbor Colossus is nice to shut down fliers for a minute, as well. What is Garruk's Packleader for, you ask? Who plays that!? Well, see, once the combo is set up, the opponent has a narrow window in which to react: a simple kill-spell like Hero's Downfall won't do, I'll just respond and monstrous the Broodmaster. (Yes, you can monstrous at instant speed, and make tokens in response to Downfalls. I asked.) Board wipes (End Hostilities and AEtherspouts being the most popular) is an option, since it resolves after the monstrous ability and therefore hits the hydra tokens... BUT, with Garruk's Packleader
+
Hydra Broodmaster
out, I can monstrous in response to their board wipe, and draw as many cards as I want until I hit a Stubborn Denial to respond to whatever they try and answer with. Maybe several if they're playing control...
