ultima weapon isnt that hard to get if you think about it. as long as you have all the lucky lucky abilities, as well as the ultima recipe, you shouldnt have a problem getting it. fenrir, on the other hand, you must simply beat sephiroth, whos not actually that hard if you have the right stats. also, if you havent gotten all the oricichalcum+'s yet, heres a way to get the one for the 1000 items:
put on all lucky lucky's. equip draw to save a little time. then go to the pride lands and go on top of the king's den. theres a swarm of rapid thruster. simply use magnega to kill them off, and watch with joy as a storm of lightning shards rains down onto your party.