Here's how I think it would play out, using the magic d12.
1. 8 (Twilight Sparkle) 4 (The Scotsman)
2. 5 (Wolfwood) 5 (Alphonse Elric)
3. 8 (Invader Skoodge) 10 (Michonne) 1 (Hei)
4. 11 (Mulan) 5 (Rorschach)
5. Zuko vs. Jeremiah vs. Sara
Round 1: Although the Scotsman keeps trying to gun down or blow up Twilight Sparkle, she is able to either dodge his attacks with teleportation or block them with a force field. Eventually he runs out of ammunition and pulls out his sword, waiting for the pwny to come to him. Twilight Sparkle fires several magic missiles, but the Scotsman dodges each one. Focusing, Twilight Sparkle levitates him, throwing him thousands of feet up in the air. He dies from the fall.
Winner: Twilight Sparkle
Round 2: Wolfwood fires his big ass machine gun at Alphonse. After Alphonse takes no damage, he transmutes the ground and Wolfwood falls into a pit. Alphonse looks into the pit to make sure Wolfwood's okay, only to be destroyed by a missile.
Round 3: Michonne fires her pistol at Skoodge's head. She then fires at Hei, and the bullets either miss or bounce off of his cloak. A knife flies through the air into Michonne's heart, and she is electrocuted.
Round 4: Mulan holds her sword out at Rorschach, who is unintimidated. She swings her sword defensively a few times, then she decides to go for the kill. Rorschach dodges her sword as she stabs at him, closes in and bites her ear off. She drops her sword as he strangles her to death.
Round 5: Sara sits, playing her guitar thing. Zuko and Jeremiah ignore the blind lady and focus on each other. Zuko throws a fireball at Jeremiah, who dodges and pulls a blade out of his arm. Jeremiah sprints towards Zuko, who sprays fire at him. Jeremiah leaps 50 feet in the air, dodging Zuko's fire. Jeremiah begins to aim his body like a dart towards Zuko, with his arm blade sticking out. Zuko throws a massive barrage of flame in front of Jeremiah, who flies into it. Zuko then does a backflip to dodge Jeremiah, and pulls out his swords. A singed Jeremiah pulls his arm blade out of the ground, and charges Zuko. Both of them slash at each other for about an hour, Zuko learns that his blades have no effect on Jeremiah and begins to tire. While Zuko is a better swordsman and martial artist, Jeremiah is stronger, faster and very hard to kill. Zuko eventually dies. Meanwhile, Sara stabs Jeremiah from behind with her ridiculously powerful spear. Jeremiah turns around and slashes her throat. Although now it looks like Jeremiah can't operate at full capacity.
Winner: Jeremiah Gottwald
Final fight: Jeremiah, Rorschach, Hei, Wolfwood and Twilight Sparkle all come into an open field. A very brave Skoodge walks in as well. Wolfwood, seeing the Cyborg across from him, fires a missile at Jeremiah. Jeremiah uses some of the Sakuradite left in him to jump on the missile, and push it away from his foot. The missile hits Invader Skoodge, blowing him up. Everyone else springs to action. Rorshach hides outside of the field and waits, Twilight Sparkle begins shooting dozens of magic missiles, Wolfwood is firing his machinegun at the cyborg running at him. Hei throws one of his knives at Twilight, which is deflected by a force field as she brings her attention to him. Wolfwood, now out of ammo fires his pistols at Jeremiah. He sees the small opening in Jeremiah's chest and fires at it, which slows Jeremiah down. Rorschach, seeing an opening gets behind Wolfwood and snaps his neck. Jeremiah then leaps forward, stabbing through Wolfwood and into Rorschach's heart.
Meanwhile, Twilight Sparkle has made a rolling force field and Hei can only run from it. Jeremiah strides towards the purple horse, and uses his Geass Canceller to nullify her magic. Hei uses this quick opening to send a knife through her neck. Jeremiah's energy becomes lower and lower, and Hei is able to Dodge most of his attacks. Skoodge, using his short size gets behind Hei, and he trips. Jeremiah stabs him quickly, but Hei sends a knife into Jermiah's chest and uses his power to electrocute him. Both of them die, and Skoodge gets out from under them as the victor.