Looks like a hoot. So here's how it works.
The plan is to cast Fling, sacrificing Malignus and copy Fling with Reverberate. This leads to an insta-kill that is very hard to stop.
Slumbering Dragon and Fog helps stave off aggressive decks, by reducing their desire to attack until they can deal lethal, and then negating that damage, usually leaving them entirely open for the return strike.
Rancor + Inquisitor's Flail are good alternate win condition, either on Malignus or Slumbering Dragon.
Arbor Elf and Farseek help ramp into the combo and fix mana for all the red you'll need. The deck might be weak to countermagic; a single counter against the original Fling means you won't instantly kill. You can still copy the Fling if this happens but will only halve their life-loss.If that happens you can always do it again later, or try to build up two reverberates for the combo (either copying their counterspell or your original fling/reverberate).
Why this deck is good: There is a lot of lifegain in the format. Decks use Thragtusk and Sphinxe's Revealation to go over the reach of most aggro/creature decks. Malignus doesn't care how much health they have, the combo reaches all the way to the top.
Weakness: Control decks are obviously a weakness. If I had them I would run two Cavern of Souls so that I can ensure Malignus can be reliably cast, perhaps siding in two more against control. The Reverberate helps protect you from the countermagic somewhat, but you'll have to play wisely in that matchup.
Removal is also problematic. At this point, I don't know how best to approach that. Malignus is proof against most burn and -X spells, but Murder, Ultimate Price and enchantments can all hit him just fine. Normally you don't want to cast Malignus until you have the combo pieces assembled but unless you have 9 mana up that still means waiting a turn to combo off. Ranger's Guile might be the answer, but whether it can be fit into the mainboard, I don't know.
Sideboard tech:Ranger's Guile holds off removal, it comes in against removal heavy decks.Increasing Vengeance increases your copy abilities and comes in versus control. You can't copy their counterspells but it sets you up to chain your fling just fine.Increasing Savagery is there for the Slumbering Dragons. Probably I can find better for this slot, but if for some reason Malignus won't work, swap him out for these and set up a fling combo on the dragons.Ancient Grudge is our answer to Witchbane Orb, which is rare to see but does crop up and will cause us trouble. Better to have it and not need it, right?
Please let me know what you think of the deck, and I welcome suggestions about the main and sideboard. For instance I'm wondering if I should try and fit in Faithless Looting to speed up assembling the combo. If I do, I might want to use Deathrite Shaman to help mana accelerate, as more land cards will be in the grave that way. Stomping Ground will likely replace Evolving Wilds but should I have both? Also, should I think about Rolling Temblor to deal with Invisible Stalker type bant control decks?
