I'm already at all character max level 99. With all void, shadow, light max. But idk how to beat challenge at basement guild. Its really hard even for "Lv 80 Challenge". Only have weapon with 2 slots. Use "paralyze" and "poison" just effect for 3 turn.
Don't tell me to repeat making a guild coin, it really boring
I didn't have much trouble with the 4 challenge battles. Physical skills are more valuable for these battles (the "unique" skills), the offensive "fatal" skills are useless (but the healing ones are ok), and applying defense down helps. I think I recall that the last battle uses up items (Full Power Powder, which I farmed, was helpful), and items to keep your characters alive. Beruna uses Healan (and in general it helps to upgrade your most used skills). Upgrade your weapons (not hard to get them up high, if if you feel like it to +100, but that isn't needed) and armor. I don't recall anything too special, just stick with the unique skills and forget about the elementals. I didn't use any seeds at all (they are still in my inventory). Two weapon slots is all I used. I never used paralyze or poison.
Even if you aren't able to obtain the best in-game premium shop weapons, you can find 5 Salvatore weapons (each with 4 slots) in the storehouses throughout the game. Equip these weapons with 100% Critical Up, 100% Physical Damage Up, 100% STR Up and 100% SPD Up fragments and everything becomes a breeze. You don't even need to grind in order to strengthen the fragments, since all talismans that can be disassembled for these fragments can be bought late-game (after the normal ending). Well, you might need to grind for money so that you can afford all these talismans, but that's more bearable than grinding for monster drops.
Defensive equipment can also be used offensively, so equip, for example, Strange Sweatshirts (increase damage dealt on the first turn by 50%, can be bought after the normal ending), Energy Scarf (increases damage dealt by all allies by 10%, one-time-only reward for beating Steward Lumlin in the secret arena for the first time) and Binding Charms (damage dealt towards enemies is increased by 5% for each alive character in the allied area, can be exchanged for Guild Coins at the arena) or Repeat Charms (up to three times per battle, after acting in combat, has a 30% chance to gain another turn).
Use all the stat boosters you get on Yumil and he can soon demolish everything in one turn by using "Piu Mosso" (lets him act three times immediately) and then "Vorpal Slash". Unlike in other Exe Create games (like "Sword of Elpisia"), I didn't even need to lower the difficulty setting in order to grind for stat boosters in the secret arena.