I'm trying to build a 2.5D Sonic game and I am having trouble on what I would need to code for it to work.

I have been trying to figure out what I need to code such as; movement, jumping, and I am not sure if I need to 3D character controller or not can someone help me out please.

i suggest u to watch “Platformers” Tutorial ;
search for Barackey platformer tutorial there is a good one ;
its a 2d but good for start ;