The biggest challenge in Monark is knowing how to spend your experience points (aka SPIRIT). You don't get a lot of experience from story battles, so you have to grind to get your characters up to speed. Even worse, you constantly have to level up low-level partners that join you in battle.
SPIRIT should be spent leveling up the Protagonist and equipping your legion units with the abilities that will assist you most in battle. You should also save the experience you earn after each Pactbearer battle and use it on your new party member to help get them up to speed quickly.
You should avoid pouring all of your experience into your units. The armor you get from battles will help bring them up to speed. The most important thing is choosing abilities that will help you in battle.
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Keep in mind that levels increase rapidly with each new act, so you will need to grind throughout the game by calling extra numbers. It's ok to be a level or two below the current story mission, but going the extra mile to have a few characters over-leveled helps guarantee victory.
This especially becomes important after you beat the first couple of Pactbearers, as boss battles can start taking between 30 minutes to an hour. Spending your SPIRIT to level your team above the boss's level will help guarantee that you don't waste your time.
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I start my day by exploring Teyvat in Genshin Impact and end it after reorganizing my apartment in Final Fantasy XIV. I am a diehard fan of N64 era games and will forever feel betrayed that Megaman Legends didn't finish. Outside of gaming, I have spend my time collecting manga, collecting anime figures, and watching anime with my naked cat.