UPDATE: YES! I found the bug, it was something in the code that reset the game flags on arcade start/story start. I don't know why it didn't trigger any other chaotic bugs before? Weird... but it should be solved. I'll upload the new build soon.
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To be honest, Arcade mode is just Story mode with a turn limit and no dialogues. You have 120 turns to beat the first 8 bosses and then one shot at beating Barion. The goal would be to finish it in the least amount of turns. My personal record for the first 8 bosses is 110 turns circa, give or take 5-6. I'd be curious to see what is the most optimal strategy, if players can find one!
I tried many times and once lost to the last boss after defeating 8 bosses in 112 turns. I then removed the Sharpen Emerald Saber on Vesper and retreated once, but finished defeating 8 of them in 119 turns and was able to complete the game in a total of 177 turns.
The Arcade mode has a seemingly strict turn limit, but it was a very fun mode to figure out the strategy. MEOOOOOOW!!!