Amulet of the Platinum Fang (Patreon)

Wondrous item, very rare (requires attunement)

A single fang—said to be from a deific dragon—hangs on this platinum necklace. The tooth itself is cracked but repaired with molten platinum, sealing it together and retaining its inherent magic. You have resistance to radiant damage while wearing this amulet. In addition, whenever a spell restores hit points to you, you also gain 1d6 + 4 temporary hit points.

Platinum Aspect. While wearing the amulet, you can use an action to call forth an instantaneous, spectral maw of a platinum dragon. Make a melee spell attack with the maw against a target within 15 feet of you, using a +10 spell attack bonus. On a hit, the target takes 2d10 + 10 force damage plus 4d6 radiant damage. Once you've used this property, you can't do so again until the next dawn.

If you're a dragonborn, you can choose to use this property in place of your breath weapon. When you do, it can't be used again until you finish a short or long rest, instead of the next dawn. If you use your normal breath weapon, you can choose for it to deal radiant damage, instead of its normal damage type.

The elderly elf was warm towards the draconic knight—an unexpected, but delightful, change of pace. She offered the sleek box to him with a nod. "Might is not always enough. Presence neither. There is one thing, I've found, which unnerves even the greatest of warriors."

His long nails—claws, really— caught the lid, opening it to reveal a large, cracked tooth inside. It shimmered with a faint glow. He looked back up.

"What is this, my lady?"

Her normally small, knowing smile then stretched from ear to ear. "A winning smile, let's call it."