All righty, here we go!
Characters you have:
Sonic The Hedgehog, Miles "Tails" Prower, Knuckles The Echidna, Cream The Rabbit, Amy Rose, Shadow The Hedgehog, Rouge The Bat, Blaze The Cat, Super Sonic The Super Hedgehog, Super Miles "Super Tails" Prower, Super Knuckles The Super Echidna, Super Amy Rose, Super Shadow The Super Hedgehog, Metal Sonic The Metal Hedgehog, Mecha Sonic The Mecha Hedgehog, Metal Knuckles The Metal Echidna, Dr. Ivo Robotnik/Dr. Eggman, Classic Dr. Robotnik, Classic Sonic The Hedgehog, Classic Miles "Tails" Prower, Classic Knuckles The Echidna, Classic Super Sonic The Super Hedgehog
Characters you don't have:
Silver The Hedgehog, Super Silver The Super Hedgehog, Burning Blaze The Burning Cat, Espio The Chameleon, Vector The Crocodile, Charmy Bee, Mighty The Armadillo, Tikal The Echidna, Cosmo The Plant, Mephiles The Dark, Vanilla The Rabbit, Marine The Racoon, Classic Espio The Chameleon, Classic Vector The Crocodile, Classic Charmy Bee, Classic Mighty The Armadillo, Princess Sally Acorn, Sonia The Hedgehog, Manic The Hedgehog, Classic Sonia The Hedgehog, Classic Manic The Hedgehog, Shade The Hedgehog, Super Shade The Super Hedgehog, Hyper Sonic The Hyper Hedgehog, Hyper Shadow The Hyper Hedgehog
Fan-made characters:
Seelkadoom The Hedgehog, Hyper Shadic The Hyper Hedgehog, Nazo, Perfect Nazo
Recoulors and repaints for all characters:
Dark, Hyper, Super, Were (like Sonic The Werehog). Also applies to the classic sprite generation.
Where to find more sprites:
The Spriters Resource.com, Google Images, other games on Newgrounds, Cosmo from Tails' Love Triangle, UberSonicSceneCreator2 for Classic Shadow, Classic Cream and Classic Rouge and a bit more
New Props you didn't add:
Tails' Tornado, The Death Egg, The Sol Emeralds
If you're REALLY clever, then mix it with all the Mario things! I've seen Mario movies you've made before, like Yoshi and his computer. Here are all characters:
Mario, Luigi, Peach, Daisy, Rosalina, Wario, Waluigi, Toad, Toadette, Toadsworth, Dr. Toadley (from Mario & Sonic: Super-Rival Saga), Professor Elvin Gadd, Goombella, Bowser, all Mario enemies (find videos of all of the Mario Characters on YouTube), Kamek and Kammy The Magikoopas, The Koopalings, The Kongs, etc.
Powerups for Mario AND Sonic:
Fire (fire Sonic is somewhere, and to make all other Sonic characters fire, recolour them), Ice, Super (Super Mario, Super Luigi and Super Yoshi are in the Super Mario Bros Z. Intro), Tanooki (it's gonna be really hard work, HA ha ha ha ha!!!), blue-shelled, and just about everything else.
Mario-and-Sonic tabs
The Sonic tab will turn into the Mario Sonic tab, and here are the rest of the pairs:
Luigi-Tails
Peach-Amy
Daisy-Cream
Rosalina-Cosmo
Wario-Shadow
Waluigi-Silver
Toad-Toadette-Toadsworth-Chaos
Yoshi (no Sonic, because the Chaos are used)
Bowser-Eggman
Enemies-Eggman's Robots
Items (merged)
So...add all this, and it'll be the best scene creator in the entire universe!