Stray Metal Jelly (Labyrinth of Touhou 2 Plus Disk)
This creepypasta-looking fiend seems to be a reference to the Metal Slimes from the Dragon Quest series. In case you're not familiar with Dragon Quest, the Metal Slime family of monsters are Slimes that are rare and incredibly hard to kill (thanks to a combo of high EVA and defenses) but are balanced out by their minimal HP and the rewards. LOT2 actually has its own version of this monster archetype on 30F with the Metal Kedama enemies, though this boss seems to be an actual visitor from the Dragon Quest universe. They specifically look like a Liquid Metal Slime but if it were rendered in a more "realistic" looking artstyle.
Anyway, if you were expecting me to do actually do this fight legitimately, then you're out of luck. This thing was so dangerous that cheesing this boss with Utsuho was the only working strategy I had. Aside from its blistering speed, this jerk will eventually start throwing out VOID element attacks as part of its static attack pattern and my party just wasn't capable of tanking such attacks. I'm amazed that people have actually survived to the end of this fight (the Stray Metal Jelly, like 6F Tenshi, will eventually run away if not killed within a certain number of turns).
The only serious attempt I made was using my incredibly over-leveled Shou (who I use for gem / jewel grinding purposes) to try and brute force the fight. Even a near level 3000 Shou with massively inflated ATK via Library Upgrades could barely scratch this boss, though... that honestly might say more about Shou than it does about the boss she's fighting.
Music is "A Monster Draws Near" from Dragon Quest
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