Catnip will make things a lot easier down there, but it would be best to avoid the likes of Elder Drake and Mega Tonberry even with that accessory. Actually, every random encounter in the later stages are bosses, so you'll have your work cut out for you, fighting them will be left at your own discretion. Also, consider it your 'lucky' day should you land in a cloister full of Mega Tonberries blocking the exits.

If you're going to fight the most powerful boss in the game (Trema) with the Catnip + Trigger Happy combination, DO NOT save your game at the 100th level, but rather do it the cloister before, so that you have the necessary preparation to bring your Gunner's HP down to critical for the Catnip effect to function. Also, his HP is 999,999, so it'll only take several rounds of Trigger Happys to nail his a** down. The way I did it, I had Yuna and Rikku concentrate on healing with their Mascot dressspheres, it was down to Paine as the Gunner to deliver the coup de grace on Trema. Took 3 tries, but I managed to beat him and got the percentage points required to obtain my 100%; incidentally, it was also my first playthrough of the game. What made it slightly challenging, I guess, was the fact that you had to go into the battle battered and bruised after fighting another tough boss called Paragon; but the Iron Duke accessory was well worth the trouble, increasing the wearer's stats immensely.

I liked the via infinto it was a good challenge not many comments from me on it because I forget half of the game as i only played it once

Lol, this is actually the worst part of the game, in my opinion…

It wouldn’t have been so bad if the battles weren’t that long. If I remember correctly, it had some of the world’s toughest fiends down there equaling long and drawn out battles. Anyway, when I finished the first 20 levels in what seemed like forever, I sat back and said… Shit! I have to do another 80 of these…?

Sadly, I did finish it… two years later, had to for the 100% completion.