During the first boss battle with him, Sigma can shapeshift into any one of his base forms from Mega Man X1-7, utilizing most of the same moves from each battle body. His elemental weaknesses are as follows:
- X1 form: Thunder
- X2 form: Thunder
- X3 form: Ice
- X4 form, with cloak: Fire
- X4 form, w/o cloak: Thunder
- X5 form: Thunder
- X6 form: Fire
- X7 form: Wind
- Wolf Sigma (X1 and Xtreme1)- Hands can morph into Wolf head
- Wire Frame Sigma Head (X2)- Attacks
- Leon Sigma (Xtreme2)- Hands can morph into Lion head-like torso
- Kaiser Sigma (X3)- Cannons and face-like chest armor
- Alien Buster Sigma (X4)- Rifle
- Gamma Sigma W (X5)- Detachable hands
- Terminator Sigma (X6)- Fires energy waves from his mouth
- Colossus Sigma (X7)- Ogre horns and waist laser
- Belial Sigma (X8)- Black horns and Sigma Blade
- "I see why Zero has so much faith in you, Keyblade Wielder. It looks like you really do have the potential I had seen in you. Our potential is limitless!" - to Sora
- "Tremble with terror! You are finished!"
- "Prepare to become space dust!"
- "This is for you!" - attacking
- "I will make you understand the true potential of Reploids!"
"Fate: Theme of the 'Professor'(X7)" plays when Sora and Zero encounter Sigma.
"Sigma 2nd ~ X6 Version" plays during the first battle with Sigma.