She's spoiled, she's prissy, she's oh so rich, she's egomaniacal, and HOLY CRAP SHE'S PACKING! HIT THE DIRT!
Since humble beginnings of simply trying really, really hard to kill 56, and failing, she's since grown quite a bit into her own, becoming the demolition expert for the Gun Clun/A-Team, and joining them in battles.
Her key weapon is her beloved TBDRLIATU(The Best Damn Rocket Launcher In All The Universe), whom she has modified heavily and expanded upon since his introduction, and with whom she has quite the attachment... really attached... really, really attached...
It's probably not as bad as it looks...
 Horrified, Pinkie Pie asks Diamond Tiara "What have we created?" "Something horrible," DT says, which seems to relieve Pinkie a bit since the filly acknowledges that "this" is a problem. DT asks what they were thinking, with Pinkie saying that the song "Smile Bomb" got stuck in her head and things spiraled from there. DT repeats herself again and again, louder and more hysterical, with Pinkie breaking down with guilt as she finally reveals the fact that they "made a giant bomb filled with glitter! It’s just a bomb DT!" and hysterically claims they're both monsters. Well, she tries to. DT interrupts her by happily attaching something to the bomb, "There! We almost forgot the stabilizer dorsal fin. That thing could have gone off target without it! Whew! We’ve got to be more careful about this!" Needless to say, Pinkie is a little dumbfounded.
[CD] As a followup to AUJ and Celestia's conversation which led to the rubber ducky "causing" explosions, Pinkie Pie and Diamond Tiara are somewhere in the distance when their glitter bomb goes off. "Oh dear Faust the glitter is everywhere," Pinkie Pie exclaims, "In every place! Every! Place!" DT points out that being nude has come back to bite them.
 Pinkie Pie managed to guide Diamond Tiara (much to the filly's constant grumbling) to turn the glitter bomb into a harmless sparkle bomb. With their creation complete, Pinkie flips the switch and the bomb is launched far away. Later, it explodes on Rainbow Dash, covering her in sparkles. +She has no question where it came from.+
[OOCO] Spike states (probably sarcastically) that he's afraid upon seeing Diamond Tiara's Partybot 5000. He should be, she says, as well as he should feel inadequate in the face of it. Spike scrunches his face in thought, which she assumes to be an admittance of defeat, but he simply asks her why she built the thing anyways. After a long pause and some attempt at explanation, she gets frustrated and loudly exclaims: "DAMN IT FIFTY SIX THIS IS ALL YOUR FAULT!" [Q] "As well you should be, you should also feel inadequate and impotent, as most males will when looking at this and realizing all of their muscles are for naught in comparison to the partybot five thousand. You are small and can never make anyone as happy as the Partybot can."
[OOCO] In another session of OnO with Spike, Changeling #77, and Changeling 42. It starts off with him asking confirmation of their goal to "defeat the coming pack of flaming wolves" by getting buckets and filling them with river water. They agree to that, with Diamond Tiara saying they'll start by going to a shopkeeper. Spike sets the scene with them going into the shop, but a guard asks them about the dead kennel and tavern owners. They all feign ignorance and Spike tells them to roll. Unfortunately for him, he rolls a 1 and is forced to have the guard drop the subject and leave. Moving on to the shopkeeper's wares, it turns out the buckets are 10 gold pieces each. 42 has 20g, DT has 30g, and 77 has 40g. 77 tries to barter for a lower price by saying they need them to defeat flaming wolves, but rolls below Spike's number check. 42 tries to back him up, saying the dog with them told them of the oncoming attack, but fails to number check as well. Annoyed by their supposed lies, the shopkeeper ups the price to 20g a piece. DT turns to threatening the shopkeeper and rolls, passing with a Natural 20 for Intimidation. The shopkeeper caves and tells them to take anything they want. 42 takes that literally and starts grabbing a bunch of potions. Spike's incredulous about them turning to robbery, but 42 says that the wording gives them a loophole to make it ok.