Wyrmstaff

Staff, very rare (requires attunement by a spellcaster)

This dark staff features a dragon coiling around a gemstone at its top. A wisp of smoke drifts from the dragon's mouth. While holding this staff, you have advantage on any saving throw against an effect created by a dragon. In addition, while a wyrmling is summoned by the staff, you have resistance to the damage type the wyrmling is immune to.

Summon Wyrmling. While holding the staff, you can use an action to summon a dragon wyrmling in an unoccupied space that you can see within 30 feet of you. The wyrmling can be any kind of chromatic or metallic dragon of your choice, but once a wyrmling has been summoned, that kind of dragon wyrmling can't be summoned by the staff again until the next dawn.

The wyrmling is friendly to you and your companions for the duration. In combat, the wyrmling shares your initiative count, but takes its turn immediately after yours. It obeys your verbal commands (no action required by you). If you don't issue any commands to the wyrmling, it defends itself from hostile creatures but otherwise takes no actions.

The wyrmling disappears when it drops to 0 hit points or after 1 hour. It disappears early if you use an action to dismiss the wyrmling or summon another one. The wyrmling uses your spell attack bonus and spell save DC for its attacks and breath weapons, respectively. Whenever the wyrmling uses its breath weapon, you can choose for the effect to simultaneously originate from both the wyrmling and the end of the staff (no action required by you), provided you're holding the staff. A target in the area of both instances of the breath weapon is affected only once.

"Seriously?!" shouted the mage. "I summoned this wyrm to fight! Not to be played with!"

"Well it's not my fault you summoned such a cutie patootie," cooed the crimson-scaled tyrant.