I think Mania Sonic is Infinite.
Why? Watch the first cutscene in game. When the magenta gem is used, listen to the sound. That exact sound is used when Infinite summoned his army of tesseracts.
Watch that same citizens again. See the five, boring looking robots? After the gem is used, look at them again. They're free. They're different. They've changed. All thanks to the gem.
Dr. Eggman does use this gem at one point, so why didn't it affect him?
The gem corrupts those who aren't corrupted. The robots weren't corrupted before using it, and now they were.
Eggman is already corrupted. No need to change then.
If you watch the Super Sonic ending, Sonic and the gem are sucked into a portal. He isn't seen after that.
The gem has corrupted Mania Sonic now, and he is sent to the Forces dimension.
Look at Infinite. See that gem in his chest? That's the same gem.
The gem can obviously travel through space and time,
so this makes Infinite's army of tesseracts and him teleporting possible.
Anyone got any more proof of this, or disagree?