I saw you mentioned cards to drop in the mainboard, here's my two cents:

• Fall of the Titans: Good card, but I don't think it fits the theme of what you're trying to do. If you're looking for removal, I'd recommend removal in white, since it tends to have the best removal.

• Wing Shards: There's better removal in white.

Some others are: Pollen Lullaby and Righteousness, they just either don't seem on-theme with your commander, or are just rather subpar.

I'd recommend removal like Swords to Plowshares, Chaos Warp, and Oblivion Ring-type effects. Return to Dust and Vandalblast are also very nice for the deck. Blasphemous Act?

Hope these suggestions helped!

Wurmcoil Engine is great for any sacrifice deck and has the added benefit of lifegain!

Did you considered the new Teferi's Protection?

And also Call for Unity might be worth considering since you'll kill your creatures anyway

Looks fun to play. Any updates?

Hey! ZorrosRage totally do! Added them to the description instead... ooops!

Added an update!

You ever considered adding Preacher to the deck? You’re basically telling your opponents to choose which one of their creatures are gonna die.

Also, fyi: thornbite staff and Gift of Immortality doesn’t go infinite unfortunately because of how gift is worded. It doesn’t get reattached until end of turn.

Hope you're enjoying the deck! Here's a few suggestions if you want from when I had mine together, tempted to rebuild it:

Mimic Vat is tons of fun in this deck. Outside of your own big creatures, sometimes your opponent self-mills something spicy and you can't resist it...

Aetherflux Reservoir is a staple, but it's pretty hilarious when you can fling Serra Avatar , gain your life back, then one shot someone (or two) with it. (Best case scenario, but Brion Stoutarm gains you life throughout the game.

Sigil of the New Dawn lets you get back those creatures you flung.

Hallowed Burial wipes the board Terminus -style. Gets around indestructible and stuff.

Taurean Mauler is a cheaper Hamletback Goliath that grows with every spell your opponents cast, I'd run both personally.

Moltensteel Dragon is a cute addition. Pay a bunch of life you gained to pump up its power to finish someone off.

Rite of the Raging Storm gets you elementals to throw every turn. Plus, your opponents get them and can only attack each other with them! Mwahahahahaha

Looks like Generous Gift would be a great addition to your Sunforger package.

Vandalblast is a staple suggestion is all.

Cheers!