Feat: Spell Gem

Inspired by the degenerate demiliches your kind sometimes devolves into, you've embedded a gem into your brow, fusing it to your necrotic flesh. This gem has been specially calibrated to hold one of the following spells: Repulsion, Scrying, or Truesight. You must decide which spell your gem contains when you take this feat; changing the spell requires retraining the feat. Once per day, you can drain the gem's magical energy to Cast the Spell without spending a spell slot.

At 18th level, you can heighten whichever spell you chose to 7th level. At 20th level, you can heighten whichever spell you chose to 8th level; regardless of which spell you chose, you can instead drain the gem's magical energy to cast an 8th-rank spell turning without spending a spell slot.