In case you didn't know, the folks over at the WotC Character Optimization boards figured out a way with which to grant a level 5 kobold omnipotence.
They are now figuring out ways to kill him. The most common one is to use time travel to erase him from time. It's wacky stuff.
Some of the other stuff is a rather confusing method of using planar breaches between the Astral and the Far Realms to live until the end of time by erasing time lines in which you die.
Here is a link to the CharOp boards.
Remember, Pun-Pun's a thought experiment, likewise with the attempts to kill him. He's also the result of a horribly unproofread book, and should not be the focus of your disbelief.
That aside, time travel has been proven not to work-The kobold will be able to sense that someone's going through time to kill him. I believe the current experiment involved using a combination of time stop and planar bubble to bring a part of the Outlands to Pun-Pun, Spire magic included.