I'll give you the answer because I like your solution so darn much, and it feels like a perfect match. It isn't who I had in mind, though! My solution was Axl!
Single model - or not, / Axl is a prototype, but many reploids with the Copy Ability were later seen
Dual weapons - with others, / He uses two pistols as his primary weapons, along with those he acquires
Third leg - for completeness, / He completes the X and Zero duo, joining them as main character
Many styles - often handy. / His Copy Ability allows him to change shapes at will
One alternate - who needs more? / He only has one armor in all three games
Two gems - shiny! / On the chest and helmet
Three appearances - not bad... / He showed up in three games: X7, Command Mission and X8
All know me - for better or worse. / As main character, everyone knows him yet not everyone likes him!
On the third part, each line was about a game.
One had the color of conflict - crimson, / X7, the fight against Red Alert
Two had a special ability - invincibility, / Command Mission, as his Action Trigger
Three was grounded in tradition - yet innovated, / X8, a 2D-like platformer that tried new things
All are located within the same dimensions. / All three titles have 3D graphics
Who am I? / Axl
The next one's yours!
The admin formerly known as Dr. Cossack.
I post musings, images and nonsense on Tumblr! I play games on Steam! Add me on either/both, and don't hesitate to ask if you want to play something with me!
"There are only three things certain in life: Death, taxes, and Teej's obsessions." ~ RisingDragon (still true in 2019!)