First game i got was heroes but first game i completed was generations

Sonic CD

The Mobile port

At the time I completed all the Mobile game ports that I had except for Sonic 4 EP 1

That honor didn't hit me til like 5 weeks ago

Sonic 4 Episode 2 on mobile when it became free in like 2018 for no reason

Sonic CD

Probably the original Sonic the Hedgehog since I did a pacifist run of it back in late 2022.

My memory is a bit vague on this one, but I'm fairly certain the first Sonic game I completed was Sonic Forces

Oh actually screw that I beat Sonic 1 GG first by like a month

Generations

Sonic Generations

By the way, there is a reason why Sonic the Hedgehog 4 isn't here.