How the hell are you supposed to beat leo without using cheat tackle?
If you're going for a no cheat tackle run, firstly it's totally fine to lose the first fight against Leo. Not only will you not lose money but you still gain the trainer level if you lose this fight specifically, since if you lose Leo gives you advice that raises your trainer level anyways.
If you really want to win, you'll want to get to at least level 13 first, fighting Sumire (the girl with a single level ~25 monster near the area with the high level evolved monsters) should be easy enough, start with a lower rank candle and have it spam Dazzle to lower her accuracy until it dies, if did not get a free burn switch to Chikepu to use fire attacks until you get one, then have a Goley in the back to spam coating to stall out the 8 turns needed to win. This same strategy also works for getting a Candoll from the are next to you (though Chikepu will probably be a better tank since it has two different attacks that inflict status effects). If you don't want to use stall tactics on Leo you'll probably want a Snaildrome instead, make sure to buy one Accuracy buff item from the tea vending machine, 4 Attack Colas, 7-10 Recovery Beans, and a ton of Guardrips (8 Safe T's also help). Your team will be a candle of your choice (big or small are fine) and a Panteey, start by dazzling the Snaildrome as much as you can before you either die or it gets a couple coatings off, then bring in your Panteey (Panteey has the cunning ability meaning that once it's out whenever it tries to raise it's own defense, it raises yours instead). Use Guardrips to ensure your defense is always +6 or higher and anytime you fall to ~22 HP or less use a Recovery bean to not risk being one-shot by Muddy Water. Buff up your attack, and if 'Mud' is ever inflicted on you increase your accuracy, and then just slowly wittle away at it's health since it's immune to status effects.
For the actual fight against Leo, If you plan to use Candoll I'd recommend 4-6 Guardrips, 8 Safe Ts (optional but nice), one accuracy booster, and ~5 Recovery beans (10 if you skip out on the Safe Ts), this should run you anywhere from 3.5k-10k in costs. I'd start by using Safe Ts against the first enemy and save the Guardrips for the second since the first enemy can lower your defense, the accuracy item is just in case the second enemy inflicts Mud on you (which it can do if you ever attack it) but even then it's not strictly required, the goal is to have your defense and evasion as maxed out keeping in mind that +8 is the cap. With this setup you should be able to survive two attacks against Leo's level 38, so you can safely use either Flame Sphere (hoping for a burn) or Dazzling inbetween Recovery beans and just stall it out until you win. For Snaildrome the strategy is more complicated, as now not only do you have to add in 4-6 Attack Colas, but since the 2nd enemy can lower your attack you do not have a perfectly safe opportunity to setup. You can use your increase hit item early so that you can guarantee inflict mud on whichever enemy you feel is safer to setup against (I found the 2nd to use attack down less than the first used defense down) but if you can manage to reach Leo's level 38 with a +6 or higher in both attack and defense, +8 evasion, and +4 hit, then open by inflicting Mud on the final monster and then between recovery beans and your comparable stats you should be able to win in several turns. The Candoll option is easier, more consistent, and less expensive but the Snaildrome option exists if you hate stalling.
For my wins, I had a 5 star level 14 Candoll and a 0 star level 14 Snaildrome, but 0 stars and level 13 should work just fine for either option. I also cannot recommend fighting Sanae (the girl in the starting village with a single level 95) just to level 14 as since she's immune to debuffs plus has a highly aggressive moveset you have to get really lucky to beat her. Getting a Garudator (same strategy as getting the Candoll) to fish for a cut proc with Wind Cutter can help against her, but it's such a massive reset fest so I'd recommend giving Leo a few attempts before going this option.
They enemy boss uses them? Well, maybe they are op
