Cold Caster
Prerequisites 4th
You gain the following benefits.
Ability Score Increase. Increase your Intelligence, Wisdom, or Charisma by 1, to a maximum of 20.
Cantrip. You learn the Ray of Frost cantrip. If you already know it, you learn a different Wizard cantrip of your choice. The spell’s spellcasting ability is the ability increased by this feat.
Frostbite. Once per turn when you hit a creature with an attack roll and deal Cold damage, you can temporarily negate the creature’s defenses. The creature subtracts dice:1d4|noform|noparens|avg (1d4) from the next saving throw it makes before the end of your next turn.
Sources
Forgotten Realms: Heroes of Faerûn p. 39