This deck functions by maximizing the value of efficient lifegain spells by turning them into damage either directly (Vizkopa Guildmage and Sanguine Bond) or indirectly (Kavu Predator, Ajani's Pridemate, and Lone Rider ). The key here is to use spells that give life to target player; this gives you the flexibility to use them in conjunction with what you have on the board to maximum effect. If you're swinging in with two Kavu Predators, it's probably best to use that Heroes' Reunion on your opponent; if you have a Sanguine Bond out, why not drain your opponent for seven instead?

This is possibly the one deck where Healing Hands isn't a waste of space; it fits neatly into our curve, can buff any of our (potentially very scary) two drops and draws us a card. Sunbeam Spellbomb is similar, but has the unfortunate caveat of only being able to target us for lifegain. Sunbeam is nice, though, because we can just leave it there until the optimum moment to crack it or cycle it for a card (I ended up cutting it in favor of going four Duress and getting in a third Primal Command, but it's still a fine option). Siege Rhino does Siege Rhino things, and pumps Ajani's Pridemate while simultaneously turning on Lone Rider . Lone Rider works very well with Ajani's Pridemate - the first strike lifelink means he will actually put a counter on our cat friend before he deals damage, which can often throw a slight wrench into our opponent's combat math. Kavu Predator is a ****ing monster with any of our instant speed lifegain spells. If you thought Invigorate was good, wait till you use Heroes' Reunion with multiple Kavu's on the field. It's still quite good even with a single Kavu, as the damage should cancel out the lifegain. You can even wait until your opponent taps out and then pump him, creating a ridiculously oversized threat that they have to deal with or they may as well concede. Sylvan Bounty is a workhorse; in the early game, it fetches us lands (functioning as lands 21-24), while in the late game it works with any of our strategies. It can drain for 8 with a Sanguine Bond out, pump a Kavu, etc etc. Very versatile card that meshes well in the deck. Duress is mostly there to strip a removal spell or a boardwipe. We only really need a couple of our creatures to stick to win, so getting any removal out of their hand makes a difference. Vizkopa Guildmage gives us a consistent source of more lifegain via lifelink and can weaponize our lifegain spells for three mana. That's not always relevant and doesn't really work with Sylvan Bounty, but it's an excellent safety valve and the lifelink is often relevant (especially since we can activate it at instant speed).

Devour Flesh is there for Boggles or just general Kavu synergy/removal, while Nature's Claim pulls double duty against artifact and enchantment decks while also providing a pump for the Kavu. We're not super concerned about the lifegain, since our own lifegain by far will outpace it and we can afford to play a long game as our creatures grow over time. Damping Sphere gives us a prop against Tron and Storm, and Nihil Spellbomb keeps the yard clear and can draw us a card when necessary.

The deck does need mainboard removal, and at the moment my goal is to test it enough to figure out what can be safely cut to make space. I'm leaning towards Oust or Path to Exile; Path is obviously better removal but it has no synergy with our deck and ramping the enemy is never fun. However, I'm not quite dumb enough to go against the modern braintrust and will probably end up using Path. Other options include Condemn (creature has to attack) and Last Breath (generally meh). When I get around to buying a playset, I'd probably put two in the sideboard over two Devour Flesh and find two more slots in the main.

Some will probably ask why Tainted Remedy isn't in the deck. The answer is that it originally was a Tainted Remedy deck, but frankly the card just didn't really make the cut. Sanguine Bond is more expensive but is vastly better, and I prefer the Vizkopa Guildmage for its versatility. Tainted Remedy also shuts off pumping our Kavus and pushes us towards using our lifegain spells on our opponent, which we normally only do when we have a Kavu out. The non-bo between those two was enough that I made a choice, and I went with Kavu, as it represents a much more efficient and potent threat. There probably is a build of the deck that would rather use Tainted Remedy, but for the moment I'm leaving it out.

I'll probably check out Nightmare's Thirst and Infernal Reckoning once M19 drops. Thirst might be the removal spell we actually want, as it would be highly efficient in our deck, while Reckoning might be worth a few sideboard slots as additional affinity/tron hate.

I considered a build of this deck using Pride Guardian, Wall of Essence and Perimeter Captain to gain lots of life and hold down the early game, but ultimately rejected it. There might be some potential there, though. If you're willing to shell out for Wall of Shards, it could work very well with Tainted Remedy. Souls of the Faultless could also work; the defender build would probably orient more around having 4 copies of each of Sanguine Bond and Tainted Remedy.

Voracious Wurm is another card I'm considering. It might end up replacing Ajani's Pridemate, or possibly I might go with a 2/2 split. I also want to find space for a couple copies of Primal Command, which seems like it would be a house in this deck.

Update: removed Kavu Predator in favor of Grim Flayer. It was just too much of a non-bo with the rest of the deck and often just sat in hand uselessly. It's still a powerful card, but the shell just isn't there. Grim Flayer gives us card selection and a strong threat in one two drop and is just the better card.

Update2: Dropped Heroes' Reunion in favor of a playset of Blessed Alliance and dropped Sunbeam Spellbomb for a full playset of Duress and another Primal Command. Heroes' Reunion is excellent late game, but unless you have a Vizkopa Guildmage or a Sanguine Bond out, it's fairly worthless other than turning on a Lone Rider, and there's just better options for that. Blessed Alliance gains less life, but it's easier to cast and has so much utility. Heroes' Reunion just sits in your hand until turn six most games, doing nothing but finishing off a game you likly already won. I also went with a 3/3 split on Ajani's Pridemate and Vizkopa, since Vizkopa's ability to give something lifelink is surprisingly relevant and it weaponizes our other sources of lifegain. I also squeezed in an Abrupt Decay for all-purpose removal, with three more in the sideboard to give us a very broad removal suite along with Nightmare's Thirst and Blessed Alliance. Molder might seem weird, but I want to try it out as an interesting option against Affinity and perhaps Bogles. Most artifacts ran by competitive decks are 2 mana or less, so casting it is hardly going to be a problem and the life gain can be relevant by putting a counter on a Pridemate or potentially flipping a Lone Rider or what have you. I might just swap it for Invoke the Divine or something similar though, since going T1 duress into T2 rider into T3 blow up something important and flip the rider seems like a very strong line of play.

Update: Dropped Healing Hands for Revitalize. It's cheaper, still turns on Lone Rider, and is an instant. Healing Hands makes more sense for a Kavu Predator/Tainted Remedy build.