This is the 3rd floor of Peach's Castle from Super Mario 64.
The characters involved are:
Samus, Megaman, Zero, Adult Link OoT, Young Link OoT, Link from Twilight Princess, ShyGuy, Sonic, Guy from Far Cry, Fat Zombie from Doom 3, Luigi, Yuffie, Cactuar, Servbot, Guilty Spark, Grunt, Master Chief, Bowser, Peach, Falco, Female Night Elf, Doom 3 Hell-Knight, Leon Kennedy, Red KoopaParatroopa, Lara Croft, Sam Fisher, Max Payne, The Terminator, Shadow the Hedgehog, Knuckles The Echidna, Amy Rose
And if you look very, very hard: All 7 Chaos Emeralds
I made this about a year ago, using Garry's Mod, of course. I really like it and I hope you like it too!
Sorry everyone, I made this picture about 2 computers ago. I do not have any links to any of the models or maps anymore. I'm very sorry.