This is a Day 10 to 12 Hard Mode score attack for the last Gremlin. Waiting until late in the game to beat last ones and fighting in chaos infusions will significantly increase gil received after battle. I'm only on my second playthrough, so I am not fighting with optimized stats, abilities, or equipment.
Like with most small scale last ones, we recommend fighting Gremlin before Day 13 so that the chaos infusions are saved for more lucrative encounters. See this topic for a discussion of when to defeat each last one: http://etrosgate.com/forums/viewtopic.php?f=9&t=234
You are guaranteed an Element drop from this fight, and there is a 40% chance of getting the chaos-infused auto-ability Multiple Targets +30%. This wasn't originally on my list of abilities to collect, but I've used it a few times since to positive effect. You may want to retry until you get one here.
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