Heres an update on my final fantasy 10 no sphere grid challenge (Basically no leveling up) playthrough.
Once you get to areas like thunder plains and Macalania, enemys pretty much all get the first turn over you, due to having higher agility which is even worse if you get ambushed, so if unprepared you can cop a game over pretty easy. Having Rikku steal in every fight she can is very important, and even backtracking to earlier places like Djose Highroad once Rikku joins to get hands on Silence + Petrify Grenades from mushrooms and anacondas helped out a bunch. They become very useful for Bikanel Island to Bevelle when you don't have Yuna in the party during that time
A decent strategy I use is I bought a First Strike weapon for Tidus guaranteeing me a first move even if I'm ambushed during random encounters, which I then use him to switch to Rikku or Yuna to deal with the monsters from there on.
Customize with Rikku is super important too when entering different areas, gotta keep stealing appropriate items to customize protection, like Lightningproof, Fireproof, Iceproof, Waterproof.
Right now, i'm up to the Calm lands, I captured all the fiends for the Monster Arena minigame (Malboro was tricky to capture, but I manged to pull it off) and I just got Yojimbo in the cavern of the fayth and captured all the monsters in there for the arena. Next i'll be backtracking to macalania and capture all the monsters there to get the 60x Shining gems reward which deal a nice amount of damage when used.
Only Auron has a bit higher hp then the starting hp (1030 Hp) in this screenshot due to a 10% hp armour his currently wearing which i also customised with Fire + Waterproof
