its 15 on his sheet, but chris states that his super mega mary sue form that he can activate anytime he wants (presumably as a free action) says "+10 to everything" and I assume he literally means every number on his sheet from skills, stats, HP, damage, BAB, and AC too. So at any point something threatens to hit him he'll pop his sonichu ball and go "UHHH I GO SUPER MODE TO AVOID THE HIT!"
So, he has an assumed +15 to every single roll, defensive stat, etc..? (Remember, he has 3 super forms and can use 2 of them at once because bullshit).
Fine. Let's fucking roll with this. He has a +32 to all rolls (5+15+12 prof), and we'll assume his every stat is 50, his AC is 30, and that this transformed state does not wear off, ever. Now we reach the point where we need some serious weapons-grade bullshit of our own to fight this. Falling damage is a max 20d6, which means that, at maximum, it'll deal 120 damage, so pits/teleportation are out. Since Super Sonic has been in space before, we'll also assume for the sake of bullshit that this technicolor abortion does not need to eat, sleep, or breathe. Finally, let's assume that his asspull magic rocks provide immunity to all types of magical damage.
So, how to deal with this? The simple truth is that I don't know how to kill this sort of creature, but we can rather easily seal it away. The Deck Of Many Things is a powerful and hilarious tool for dickslapping egotists and was basically designed to sucker tards into killing their precious Mary Sue. The Deck's positive cards either won't help Chris or are basically worthless compared to his super Mary Sue equipment, and of the negative cards, Donjon, Flames, Balance, Void, Ruin and Talons would be hilarious.
Balance would affect Chris the least since we all know he's not exactly going to be roleplaying a Neutral Good character, probably skewing towards Neutral Evil or Chaotic Neutral at best. But this would force his alignment out of order of his God's, and therefore he would effectively Fall as a Cleric (which is something that can happen.). This denies him his spellcasting. Flames would cause a powerful devil to hate him. Maybe Mephistopheles? Orcus? An'grath from 40k? The possibilities for dickery are endless.
Ruin and Talons are fun as they would remove all his magical items. This means no more transformations, no more anything. Ruin would be more deadly as it would deny him everything at all, but considering all the magic items and the fact that they've been established to be needed for transforming, it means negating his stat boost bullshit.
Donjon and Void are the "fuck you, you die" cards. No save, no magic, no bullshit, you need a new character. Or you can have fun roleplaying screaming in a dark and tiny cage for eternity.
The only card that could be considered useful to Chris would be Moon, which grants 1d3 wishes, but this is a by the books gamble either way.
Alternately, a high enough level Wizard can use Wish and Simalcrum to duplicate himself infinitely. Now, each and every one of those Wizard clones can use Enervate, but twist it to be 3e style. Let's say Maximized Energy Drain, which inflicts 8 negative levels a pop.
Let us assume that this wizard has created his Clone Army of himself plus four Simulcra of himself. On their turn, (they will survive any divine magic hurled at them, and even if some don't, it's irrelevant), their target takes 40 negative levels without save or means to resist this. A creature that has more negative levels than their HD dies. We can argue that technically Chris has 2 HD and therefore would die from just one Energy Drain, but I'm assuming he has 23. Either way he dies.