X-Men 2: Clone Wars/Sentinel Complex

This segment consists of four stages. The first stage is the lower level of the complex, the second is the upper level, the third is the Sentinel Core (where you face the first boss), and the fourth is running the second stage backwards to escape the exploding building.

Sentinel Core
The first boss of the game is a stationary computer inside a Sentinel. At the botton of the enemy lies rotating energy blocks which power the computer. You must destroy every block attached to the computer in order for it to be destroyed. While you attack it, it sends streams of electricity from the energy blocks as well as energy emission from the "eyes." Distance fighters such as Cyclops and Gambit work well here, or place Nighcrawler as far right as possible, crouching so that the electricity streams pass harmlessly overhead and simply teleport on the spot when the core fires an eye beam at you.

After the core blows, head back the way you came.

Escape
Once you exit the Sentinel's mouth a countdown timer will start. Go back along the paths you took to get here. Your goal is the emergency exit to the right of the elevator where you started this part. When you get there just run right past it to leave the complex.