Multiple suggestions, Ability might be renamed by the mod creator as see fit.

Piston

When placed on boots: Fall Damage Reducer (I would have said slime boots, but has been suggested)

When placed on Chestplate: (Show on arms) adds Knockback to bare punches

Silky Jewel

Silk Body: When attacked by mob, raises the chance to drop their statues, durability is cut in half.

Enderpearl + Obsidian

Self-Mutilation: Helmet only modifier, when player dies they drop their own head.

Pumpkin

Jack-o-helm: Helmet only slot: Prevents enderman to get aggro when looked at. Blurs Vision with pumpkin blur.

Dragon Head

Drag-o-helm: Same as above but no blur.

I'll consider the Pumpkin modifier, but probably not the other ones.

np, though was kinda mostly making a parallel with TiCon with some modifiers, with some extras using vanilla mechanics (Pumpkin), and perhaps a use for the dragon head (not many mods uses it).

I tried to make the pumpkin thing work, but the necessary checks for this are hardcoded into the Enderman AI routines and locked behind a package-private inner class. Preliminary ways I've tried to work around this haven't worked, so for the moment I'll let sleeping dogs lie.

Ok no problem