This is Umitrin (alternatively called Ametrine). She is a corrupted Quartz who was friends with Gomedha. They were separated about 4000 years ago when Gomedha went out to explore the world instead of staying up in the mountains.
Despite being a Quartz, Umitrin actually has a very gentle nature. While she probably killed tons of Gems during the war (in which she fought on the side of Homeworld), she actually has a heart of gold and if she’d joined the fight any earlier than she did she probably would’ve ended up switching sides before the war ended--she was actually considering it.
As a corrupted Gem, she mostly spends her time being a big warm cuddle pillow for other social and relatively passive monsters while also chasing off major threats like aggressive monsters and the Crystal Gems. She once flung Garnet several miles away with her horn. She strong.
Her concept design was pretty similar to this before we started seeing corrupted Quartzes in the promos for week 3, Umitrin’s final design was given only minor changes compared to her original look to match because I thought “why not lmao”. I’m still in disbelief over how close I was.