Playing the through the game again, since the 1.0'ish release. I have a little tip for anyone wanting to win the first Leo fight without cheating for the heck of it. The dev deliberately left an out in Leo's team setup. As you'd have been 1-shot by the lvl 36 yarimon otherwise. The weaker ones allows you to buff yourself a lot beforehand. The level 36 one is fire based. One of the best tanks in much of the game, especially after Moostar's nerf is (Moostar is still the best in my opinion) the yellow slime called "Slorp/Snaildome". It's immune to status effects, which is the big killer in long fights. The slime also has type advantage against Champlio.
A money mushroom (red/yellow) occasionally spawn in the little area in the middle right of the map. You'll need a few of the red ones on top of what you already have of money or get lucky with a yellow mushroom. Buy guard, attack, and hit potions. Evade potions wouldn't hurt either, but it's not obligatory.
There's a green mushroom in the dangerous area (bottom left) of Road of Beginnings.
You CAN defeat the level 28 or something trainer to get access to the green mushroom. The opponent wastes many turns trying to apply status effects on you, of which you are immune. You just have to get lucky for it to do it enough times to have your defense build up. The number next to the stat highlighted is not a turn counter, but a stack counter. You can stack a stat buff a max of 8 times. Potions lasts the entire fight. Get your yarimons to level 11, which if I recall correctly is the highest at that point without cheating. The trainer in the place to the North (Old Road) of Road of Beginners is simply too strong. The legendary trainer in the starter town is not a possibility without cheating. Buy buff potions in the vending machines found in the Northern part of the Road of Beginners.
Using whatever method, get a damaging status effect on the lvl 28 (or something) trainer's yarimon. Something on hit and resetting until it happens kind of thing. Have the slime be next in line. Then buff it with Guardrip (defense potion) and heal the slime every time it takes a hit. Adding further Guardrips in between. Might even add a Safe-T (evade potion) when at full health and fully buffed defense. The trainer's yarimon will sooner or later go down. It might take quite a few tries, but it will work.
You can use the same method on a "low" level (around lvl 25) Snaildome found in the area and capture it. Sure the level will be decreased to your trainer level, but it has a better stat line than it's pre-evolution version.
Now farm until you have 10 stars on your lineup (100 fights). Rearrange your yarimons making your Snaildome first in line. Farm some money mushroom if neccessary. Buy 10 of each potion except hit milk (you should still buy a few of them). Why 10 if 8 stacks is the maximum and the fact that potions adds 2 stacks each? Because Leo's Yarimons will debuff you every now and then. Requiring further buffs.
The whole process is agonizingly boring and it doesn't reward you in any way. Except a bit of selfsatisfaction it provides and a cheeky middlefinger to the game. For daring you to cheat or "wanting" you to lose. You get the same reward for winning as losing in this fight. Both provides you a trainer level and no sex scene (as there were no wager).