Did some general nix playtesting and came up with the new posted list.
Main Deck
Out:
1 Boros Charm
In:
1 Selesnya Charm
Rational: Evening out the charms give you a more consistent creature base, another big removal and another trample source. Still have 5 sources of double strike between the Boros Charms and Ajani. The flash creature can counter devour flesh.
Out:
4x Fleecemane Lion
In:
4x Bassara Tower Archer
Rational: Lions did a lot of work with their 3 toughness but they constantly die against mono black or get bounced in the blue control match up. Their monstrosity can be game changing against control but I'm only had it come online and make a difference maybe once in all the games I've played. Most of the time you end up with 5 mana locked out waiting for them to kill/bounce it/tap out so you can respond with monstrosity. Bassara are just far more consistent early game with their hexproof. Flyer blocking is something this deck didn't have previously so that's just gravy.
Out:
1 Plains
2 Forest
3 Temple of Triumph
In
4 Mana Confluence
2 Temple of Abandon
Rational:
Mana confluence is a no brainer. This deck always had the potential to leave your hand dry of creatures or of the wrong mana for what you did draw, Mana Confluence helps in a big way. The temple of triumph -> Abandon swap is due to the critical nature of hitting green with both bassara and Witchstalker. Losing some white does hurt Fiendslayer Paladin but getting out Bassara and witchstalkers is generally more mission critical. May be worth cycling out the fiendslayers for something like Ghor-Clan Rampager.
Sideboard:
Lots has changed so I'll just address every card fresh:
2x Gift of Orzhova - For burn match ups or ones where the evasion can eek in the last points of damage (UW control for example)
2x Mizzium Mortars - Blood Baron and Stormbreath matchups. (Expensive) wipe versus weenie.
3x Skylasher - Mono Blue and UWx control. Semi hexproof in this matchup and guaranteed to hit the board, perhaps right after a board wipe.
2x Banishing Light - Chained to the rocks 5 and 6. Prefer this over oppressive rays since it hits plainswalkers, enchantments, and gods. Downside is that it's hard to cast an offensive enchant AND this in the same turn.
2x Aegis of the Gods - Mono black / Esper. G2 they likely cycle out target hate for devour flesh, duress, etc. Aegis comes in and directly counters that strategy.
2x Ajani's Presence - Strictly better than Mending Touch. Regenerated creatures come back in tapped and are susceptible to follow up kill effects. If they were attacking they don't deal their damage, whereas here they will. The +1/+1 may be relevant occasionally for killing something they block with or for finishing out the game. This deck loves to get people to 2 health so 1 more damage for your double striker is great. The strive is just gravy. Maybe you save 2 creatures from a supreme verdict.
2x Deicide - Mono blue hoser. Should also stem the early tide of Iroas, God of Victory *list* and Atheros god of passage and who knows what else. You also get to see their hand and what they boarded in in their library when you exile a god which should help you make the choices needed. Short of gods, enchantments are still a thing and something like Dictate of Erebos will absolutely hose this deck unchecked. If dictate becomes a mainboard mono black card, we may have to main board this.
Future Considerations:
Not a fan of the Fiendslayer Paladin inclusion anymore. Hard to cast and really slows you down outside of mono black and burn. Now with 12 true hexproof creatures they may have worn out their welcome (although losing the lifelink vs. burn could be painful). I posted a list in my maybe section, most of these are the 2 ofs that I think have the potential to replace fiendslayer. My two considerations atm are realistically Ghor Clan for more burst or Voice of Resurgence for board wipe resilience.