I have only two challenges left - Jimmy Jenkins and Ride Together, Die Together...
I've seen Tumbaa every single time I've gone to the WEP. Never Pimon, regardless of my number of players. Is this an xbox only glitch? Or was it patched alongside the lyuda (I only see guns as "White Death" rather than "Lyuda" still due to the length of my save game; perhaps this glitch is also a matter of your save game)?
On one character, I've seen Tumba about 10 times, never seen Pimon. On another though, I've seen both at once about 5 times. On both Normal and TVHM. And both having done save and quits to reload back at the Natural Selection Annex.
I'm starting to wonder if it's bad luck, or if there's a glitch somewhere that stops him from spawning.
Well, I just saw Pimon for the first time in my game.
On my main character (Xbox live account, completed all quests, playthrough one) I never saw Pimon.
I made a new account a while back, made a character on that new account, and set that new character to be player 1. I then ran through the entire story again until I made it to the preserve. The only side quest I accepted was Doctor's Orders for Tannis, and this was my first time through the area. I ran through the spot where Pimon and Tumbaa would normally spawn, then entered and exited the Natural Selection Annex (after killing everything there and not seeing a single one of the two), and voila both Pimon and Tumbaa were in their respective spots. I then proceeded to kill them.
Although there are a lot of new variables introduced, I think that the most likely cause of Pimon's sudden appearance is the creation of a new character. I think it is a save-linked trait.