As a former warrior and current Death Knight, Doommuffin is quite proficient with heavy two-handed weapons, favoring swords. Actually, it's quite comical to see her wield them up until she starts slaughtering things.
When she was much younger, the then Aria had already begun to learn how to be a mage. As such, when she became a Death Knight, she proved quite proficient in the necromancy side of things. Though this, she can empower her weapon strikes, cast damaging spells involving icy disease or pure unholy energy, temporarily reduce the effectiveness of magic in a sphere around her, and even temporarily raise the dead! It's not a pretty sight when she does that, though, and she doesn't like to do it. In short (pun not intended), she's an Undeath specialized Death Knight, though instead of having a ghoul pet constantly, she has a ghost cat.
To call Doommuffin's other primary skill 'tinkering' is a bit of an understatement, even if that's the term she would use to describe it. She is a true Gnomish Engineer. Explosives, robots, strange devices, you name it, she can make a very cludgy version of it! This is, however, Gnomish Engineering at its finest. Which means there is always a major flaw to temper her wondrous inventions. In practice, she usually focuses on robots that are in turn possessed by her ghost cat Deathcake.
Aria Silverfingers was born to a long line of gnomish mages. Raised with high hopes, all expected her to be yet another wielder of the arcane! Then the Second War happened, and everyone in her family went and hid in Ironforge while orcs looted the rest of Dun Moragh. I'm sure Gnomeregan was fine. Stuck inside Ironforge, Aria watched and learned of these wonderful, yet simple... wonderfully simple combat techniques of hitting hour enemies with large blunt and/or sharp objects! Orcs loved it! Dwarves loved it! Surely these two other races were on to something!
And so, much to her family's distress and dismay, 28 year old Aria (that's like being in the early teens to a human) turned her back on learning magery and began to train with the dwarves, learning the fine art of smashing enemies with physical force instead of the vast powers of the arcane! Of course the dwarven children in her training classes thought she was hilarious and adorable, and never thought the little gnome would really match up to dwarven standards. Aria, of course, proved them wrong. While the dwarves all learned the usual techniques, Aria learned different ones in addition. Leverage, agility, and of course with training she was much stronger than usual.
Proudly, her trainers declared her fully trained, and she walked back to Gnomeregan feeling 4 feet tall with pride! Then the Troggs invaded. Like, the same day. While Aria fought vailiantly alongside the other defenders of Gnomeregan, soon things went from bad to worse in rather ledendary ways that only gnomes can pull off. Long story short, Gnomeregan was left completely uninhabitable, and everyone limped back to Ironforge, where they found out about that whole 'Third War' thing that was going on at the same time. Woops. Now a member of the Alliance, Aria continued to have adventures across Azeroth for a while. Still, she felt just a little guilty for not having been involved in the third war proper. When Naxxramas showed up over the Plaguelands, seeming to herald a new Scourge invasion, she joined Ardent Dawn and fought this new, lesser scourge invasion, continuing to hold the lines while others went off to Outland to fight the Legion there.
And then she went and got herself killed.
That's not the end of things, of course. When the Lich King gets involved, that's just another step in life. In preparation of attacking Light's Hope Chapel, a new army of Death Knights was being raised. And wouldn't you know it, but Aria was one of them! It was here that she started to earn her new name. An orc trainee was taunting her, calling her a little muffin. He didn't pass muster. She did. She was his doom. And thus a new nickname, one she embraced, was applied to her. New Avalon was soon destroyed, and this new Death Knight army marched on Light's Hope. Things didn't go as well there. Or did they? It all depends on your point of view, but at the end of it all, Tiron Fordring held Ashbringer and Darion Morgrain created the Order of the Ebon Blade to fight against the Lich King in Northrend. Rejoining the Alliance, the gnome now known as Doommuffin fought loyally for years, across the campaigns in Northrend, the shattered Azeroth, and into Pandaria. But before all these battles, he started by raising her beloved pet cat as a ghost. Girl's gotta have priorities.