I had a lot of fun with this. Just a lot of effort going into everything.
Only critique would be the last boss fight. It was done so quickly, even though it´s supposed to be the finale. The Soviet Rangers had a better fight (a real enjoyable one at that) than the final boss, which leaves you a bit disappointed? Like I was so hyped at the fused giant Mecha fight, I loved figuring out that I can extinguish the fire by rolling in the snow, but the last fight, the thing the player will leave the game with... didn´t have such a highlight. So maybe, next time plan the last fight at the beginning to have a goal to work towards? Or keep in mind to make it the highlight instead of the fights in the middle.
She could have caused a small earthquake with her purr or turned into a giant cat chasing you. Maybe lunge attacks or a second phase where you have to avoid stuff during her ult, because you can´t stop it and can´t attack her. Just to make her more threatening.
But you could just shoot her and she was dead... She was kinda the weakest boss.