Oh mean I've waited so much for this! And I'm the first one to sign up too! Sweet!
Alt mode: Dragon
Weapons, abilities: One greatsword, two pistols, along with his more than average strength acquired as a result of his years of training at the Thunders of Iacon and the massive experience in the arena. He also has the usual dragon powers stuffs like breathing fire (in dragon mode only, of course), fire and heat resistance, thick armour, flying (although he can't unfold his wings without transforming), etc.
He also has an experimental device called the SHASC ("Shielding, Healing And Shooting Chestplate"). It is a chestplate looking something like Toa Iruini's chestplate, but bigger and with some extensions that cover the shoulders and the sides of the body. What it does is simple: it can absorb any form of energy that comes to the user (including kinetic), it can absorb it, and then depending of the user's wish it can either use it to heal his wounds or shoot it back. It can't store it tho, or at least not in big quantities. Not to mention that threre is a short cooldown of around 3 minutes to it.
Name: Wildsong (or just Song for short)
(these two are not my photos, credits to whoever made them, cause I couldn't find them)
Alt mode: Also dragon
Weapons and abilities: Besides the dragon abilities that I listed above, she has four long knifes and four blasters. She also has two spike cable things that come out of the shoulders and that can extend or contract to stab the people around her. Her armour is not as thick as Gronius' tho.
Wildsong also has a Minicon partner named Giffin, that she met in the arena shortly after she and Gronius got captured.
This is how he looks like, but with his kibble resembling an air craft.
Alt mode(s): mini-cassette (Although he can't actually plug with anybody (yet at least)), small air drone.
Weapons, abilities: a vast
intelect, although he can't really fight, reason as of why he always hides in the corners of the arena to protect himself of the other gladiators. He is quite fast two, and he has two small blasters to help him, in addition of multiple ustensiles that he brought from his crashed ship.
In addition, shortly after she met Wildsong he got attacked by Thundercracker and his goons, who were also fighting in the arena and were trying to get the SHASC from him, thinking that it might help them get out of there and be free. The plan failed, as Wildsong came in time to protect them, but he still got severaley damaged, leaving him mute, only able to talk in R2-D2-style of noises.
If you really want to understand them, I recommend you read these.
Gronius and Wildsong are twins. They lived their entire lives on Cybertron. As Predacons they were often discriminated and hated by the Maximals around them, but while Wildsong was able to ignore them and to make herself a stable life, Gronius wasn't as strong.
He entered in this top government organisation called the Thunders of Iacon, which was basically some sort of combination of CIA and SWAT. There he was trained in battle strategies, information gathering, and others. However, even there he couldn't find himself a stable career, as the company was predominantly made out of Maximals, including their boss.
Gronius eventually got into a mission in which he and some other agents had to guard the SHASC prototype as it was sent from one point to another. Gronius was the sole survivor, as the mission was attacked by a rogue ToI agent that now was part of a criminal band called the Slayercons.
Gronius, although heavily thrown to the corner by the ToIs, who were trying to find a way retrieve the weapon, eventually found them and against the odds beat them. However, this happened to a cost: the rogue ToI attempted to backstab the other Slayercons as he took the SHASC on a ship and tried to leave Cybertron. Wildsong and Gronius went after him, fought him in the cockpit and accidentally activated the speed of light, and killed him.
However, before they could celebrate the ship entered in the middle of an asteroid field, got damaged, threw the two into temporal stasis, and brought them into Vex territorial space, where they were captured and put into the arena.
From there their stories get more liniar. Gronius tried multiple times to get out of the arena and he always was this close to do it, but he always failed. He eventually was thrown into a battle against one of the bloodiest gladiators that Iota had: Skywarp. He won, winning the respect of the arena, public, and hopefully Iota. That is the moment when Gronius realised that he doesn't want to go, that it would be better for him to stay in this arena instead of returning to Iacon where everybody hated him anyway simply for existing.
Song didn't really fought in the arena as much, tho when she was she was always winning. Her main activity was helping Giffin with his whereabouts. Giffin was a regular Minicon who, just like the two Predacons, accidentally crashed in Vex space. In the process his two Minicon brothers, Spokes and Skorn, were thrown into permanent stasis. They are alive, but they are connected to some life systems improvised by Giffin and Song together with the SHASC to keep them alive, as the Vex would not allow them to put them into any sort of CR Chamber. Song promised Giffin to try to defend him so that he could take care of the bodies, and allowed him to use the SHASC as much as he would wish.