Funny you should mention Carbuncle and Doomtrain.

If you missed carbuncle (which is strange, becuase you would be done with disc 1 probably) then you'll have to wait until disc 4 to retrieve him, but doomtrain can be gotten in disc 3. Cerberus also has status protection, but he's at the end of disc 2/beginning of 3.

I think pandemona is the first gf with spd junction, and she's in disc 2.