Mega Man X Legacy Collection

Sigma: have the sword ready and use the 2 shots so your sword is your next shot. Your can't use zeros sword while attached to the wall but you can do it midair. What I did was wait 1.5 seconds to hit him exactly when he fires his 1st shot. You take a hit but he loses half his health if done right. Then hug the high walls, double air dash to him and get ready to get your next hit in on his back.

Kaiser Sigma: is his 2nd form. He packs a lotta punch and I think is far tougher than Sigma's final form in X or X2. If you have Zero's sword that kills him in 2 hits but it's really tricky to hit him with it. When aiming for him only a charged up X-Buster shot damages him and only if it hits his head. It has to completely avoid his chest though as that negates it. Watch out for his shoulders as they block a lotta shots. Missiles in his back do massive damage, avoid at all costs. Focus on avoiding mostly and get in a hit here and there. Laser does damage fast so stay outta it. If he's shooting it high then skip attacking him as you'll take damage. I hit him with a sword for final damage but it's super tricky.

Achievement will pop as soon as you defeat him.