could somebody please tell me about the Jason Stryker arc?

Basically a few months after the events of X2, he made his way to an underground section of the base and activated the MasterMold (a giant sentinel factory) in roder to finish his father's work of destorying all mutants.

You see, before Weapon X, William Stryker collaborated with HYDRA to create a elite series of robots. What HYDRA didn't know what their true purpose. This project was put on halt when Styker started work on the Weapon X program, and left the sentinels as a last attemept (project Wideawake) in case Dark Cerebro failed.

Anyway, while Jason was making his way to the MasterMold, HYDRA agnets arrived at the base to try and retrieve and cover up the sentinel project, and later by the X-Men who were going into retrieve the stolen components of Cerebro that were used for the Dark Cerebro. Jason used his powers to haunt Nightcrawler/Kurt with a ghostly version of his child self (a boy version in the game). Basically he kept telling him that "HE left him to die", guilting Nightcrawler.

Jason, in control of the MasterMold and Sentinels, sent them to Hong Kong to try and destory a device created by HYDRA that acts as a EMP (a device used to disable electronical devices). The X-men and Bortherhood ended up beating him to it and disabled the outer defenses, allowing them to enter the MasterMold. Sabretooth was senmt in by magento to try and retrieve Jason for him, seeing him as a new member of the brotherhood, while Wolverine, Nightcrawler, and Bobby were sent in to destory the MasterMold. Nightcrawler once again started having visions of a young Jason, but this one actually helped him get to the main controls where the *Actual* Jason was.

As it turns out, there's two personalities of Jason. One being the evil mutant hating monster (seen in X2) and the other being his true self, locked away by the evil one. This true Jason wants Nightcrawler to help end this, as he's caused too much damage (similar to Jean feeling about her Pheonix self in X-Men 3).

Evil Jason tries to stop Nightcrawler by creating another illusion, of Nightcrawler in hell, being told he's not a mutant, but in fact a demon. Nightcrawler not beliving this, is able to break through his illusions and stop him. Just then, Sabretooth comes in to retrieve Jason, but ends up gettign caught up ina rematch with Wolverine. Nightcrawler teleports himself and a dying Jason out of the MasterMold as it starts to fall apart. Outside, the Good Jason spirit appears again and thanks Nightcrawler. Nightcrawler apologizes he wasn't able to save him, but Jason says "It's okay. You didn't leave me behind, you saved me Kurt. Thank you", and disappears.