True 20 for classes, can use fantasy paths, even the creation methods if you want to tweak.
Mind you, having a look at the True20 magic system, it’s a bit flavourless and dodgy. But I think I can fix that. Even a vancian system isn’t too bad as long as there is flavor
OGL Ancients armour on top of defense- so if you don’t beat the “to hit” by the coverage number you get the appropriate damage reduction.
3 extra feats-
Between the cracks:
When you use a Piercing weapon with finesse you get to subtract 2 from coverage provided by your target’s armour
Slice the Armour
When you use a Slashing weapon you add 2 to the damage you do to armour
Any time your armour is providing you with coverage against a weapon that is partially bludgeoning you add 2 to the coverage of your armour
Main changes in True20:- minor increase in feat progression and more starting feats for some classes. 2 more skill points per level. No Prestige classes. A strong emphasis on not multiclassing (there is total class building for those that can’t find a class that fits). Spells are feats.(sort of). Conviction replaces alignment and provides hero points. Even progression, better balance.
Not sure about heroic character arch-types. Seem to just provide some more uses for conviction and some differentiation of roles. Might need some more roles or different names.
Add Iron Heroes regional traits for humans only.
Permanent Magic: Iron Heroes “magical items” and Melnibone “demon-gear”, Weapons of Legacy, crafting of exceptional things from exceptional materials, charms-magical buildings-constructs and similar effects based on the will of the creator- the conan rule: the caster dies, the magic fails, alchemy.
Magic organized into schools based on local knowledge. Astronomy, Tarot + other divination, Alchemy, Summoning, Miracles, Turning, Rebuking, Necroscope, Telepathy, Possession/Binding/Spirit Channeling,
“Empire” realm system.
Monsters from Call of Cthulhu (as well as the basic ones)
There will be plenty of templates floating around that can be acquired based on diseases, curses, titles and mystical sites.
A bronze age, young races world, late Mesopotamia (Sorcerer King, Gilgamesh etc)
Early greek city states, some asian and conan influences (sort of Ancients Plus), a bit dark sun. Rather than “dragon kings” however we have a couple of Iron Kingdoms dragons, some titans, a demon prince, living priest god-king, lich, an epic minotaur, etc
Also a bit Talislantia
Devils as a single truenaming race.
DnD pantheon + gith + devils + elder gods
Bronze is the basic gear
Iron is generally masterworked, used for longsword and above sized blades. Some items such as a greataxe can be any materials. Iron also bends occasionally. Then there is steel, mithral, adamantite, red-steel, green star-metal and other really rare materials.