X-Men: Evolution Season 3 Episode 9

Under Lock & Key

Mesmero mentally controls Gambit into stealing half of the Spider Stone from Angel and is then captured by Magneto. Magneto finds out about the three keys that can free Apocalypse and tracks an escaping Mesmero to London. Angel goes to the X-Men for help and they pick up the trail to London as well. The two teams fight but Magneto finds and joins the two halves, which create a energy-spider. The X-Men set out to capture it while Magneto's team try to destroy it, weakening it down long enough for Magneto to eradicate it. Xavier reveals that Mesmero intended Magneto to destroy it all along - the spider was a guardian. Now the teams must find Mesmero before he acquires the third key and finally frees Apocalypse...