The developers of Honkai: Star Rail have released a video that clearly demonstrates what Tribby is capable of in battle.
Tribby is a Quantum-type character who follows the Path of Harmony. When Tribby uses her basic attack, she fires her rocket launcher, dealing Quantum damage to the target enemy and nearby targets.
When she uses the skill, Tribby gains the status of Consecration for several turns. The piercing power of all types of allies' resistances is increased.
Using her ultimate, Tribby activates a zone and deals quantum damage to all enemies. While the zone is active, enemies take increased damage. When an ally attacks, for each enemy hit by the attack, Tribby deals bonus damage to the target with the most health.
When allies use their Ultimate ability, Tribby performs a bonus attack, dealing Quantum Damage equal to a portion of her Max HP to all enemies.