- The NOAUTOAIM flag, though it is deliberately restricted to affect only missile attacks
- The Grenade Launcher's function, in a parameterized form
- The RandomPowerup effect, in a generalized and parameterized form
- The Rune system, but using normal powerups rather than runes -- so you'll want to use Powerup.Type instead of Rune.Type.
- The BUMPSPECIAL flag.
- The red armor's protection against fire.
Skulltag features not implemented:
- The "max health" increase through bonus items.
- Spread, reflection and prosperity runes. My assumption is that they would have been added long ago if they were wanted.
- All gamemode items -- skull pillars, flags, and so on; but also the Terminator and Possession Stone.
- The FloatyIcon used for medals and other messages. Not needed for ZDoom, obviously.
- The EXPLODEONDEATH flag. I don't know what it does and I handle it as a dummy flag.
- Hissy. Doesn't seem useful.
- The path nodes. Used by Skulltag's bots I suppose, which aren't the same as ZDoom's, which are deprecated anyway.
- PowerTranslucency -- instead, the invisibility sphere is made to use PowerShadow.