Core of element

When you gain this feat, you have to choose which core do you want to get from the cores below.

Core of force: you gain +1 in Strength modifier, +1 to one weapon you are proficient at that use strength and force resistance, if you had resistance to force damage before you gained this feat, you gain full immunity to force damage.

Core of radiant: you gain +1 to Dexterity modifier, if you get harmed by damage based on Dexterity saving throw, you take half as much damage on a failed save or quarter as much damage on a successful save, or else, you get resistance to radiant damage, if you had resistance to radiant damage, you gain full immunity to radiant damage.

Core of psychic: you gain +1 in Constitution modifier, you can't be affected by nonmagical condition that rely on Constitution saving throw, additionally, you get resistance to psychic damage, if you had resistance to psychic damage before you gained this feat, you get full immunity to psychic damage.

Core of thunder: you gain +1 to Intelligence modifier, if you are a spellcaster, you get +1 to spellcasting modifier and resistance to thunder damage, if you had resistance to thunder damage before you gained this feat, you get full immunity to thunder damage.

Core of acid: you gain +1 to Wisdom modifier, if you are a spellcaster, your DC get +1 and get an additional resistance to acid damage, of you had resistance to acid damage before you gained this feat, you get a full immunity to acid damage.

Core of necrotic: you gain +1 to Charisma modifier, if you are Warlock, Sorcerer or Bard, you get +1 cantrip and +1 spell from the necrotic category that you can't change in rest, this spell can be used once until you finish a long rest but don't cost any spell slot and you get resistance to necrotic damage, if you had resistance to necrotic damage before you gained this feat, you get full immunity to necrotic damage.

You can choose this feat again if you get to the right level to get another feat but you have to choose another core than the core you picked before, that means that core can't be choose twice no matter what.