Sometimes, even after a second chance has been thrown away- whether to selfish greed, or to keep old promises- it isn't the end. Sometimes a third chance will present itself, a whole new opportunity to start anew. (Portal 2 Crossover)
During Wheatley's time in charge of Aperture Laboritories, he manages to dispose of a Turret who was bothering him. What he didn't know is that he sent the turret into another dimension.
After Sparker and Dinky rescued Derpy and Chell from the Cantelot Crystal Caverns, life returned to normal. Until the consequences of their actions caught up to them. Luckily, Derpy has the solution.
Spike is trapped in a crazy research facility controlled by even crazier A.I.s. He is also is trying to get out, but with the crazy A.I.s will be impossible
Sequel to My Little Portal- Friendship is Science. Before Fluttershy dies, she hears some disturbing news. Celestial Science is being built in her world. It's a shame the mane six won't be there to stop it.
Wheatley has been in space for quite some time now. He and the other cores which had been used to corrupt him receive an offer to return - On one condition. They must establish peaceful contact with an alien world. It goes as well as you'd think
Doug Rattman and his trusty Companion Cube in Equestria. (If you don't know what I'm talking about, look up Portal 2: Lab Rat. It's bridges the gap between Portal 1 and 2.)