its hard..but not impossible.its has ridiculous amount of hp...but 6th floor is more insane tho..the bat boss has 3x the amount of tentacle boss hp and it can pass thru wall....btw i solo that tentacle in single player :v
The tentacle boss is quite easy to solo. All it took me was 14 iron bows and 840 arrows, give or take. You need to build a rectangle with wood walls and another rectangle inside it, but make sure there is 2 blocks of empty space between them. Then simply lure the tentacle boss into it, close the space in which he came in from and simply run around the rectangle while shooting him with iron bows and iron arrows. I can make a wikia guide on every boss except the final bats. That stuff is ridiculous.
Nothing wrong with the scaling. The wiki page suggests that it's the final boss, of course it is supposed to be hard. You can use haste potions/horses to go fast and maybe kite the bat, possibly even poke with a good sword. It is supposed to be an endgame boss, and let us remember the Queen/King from Pixel Survival 2. They were almost impossible to do without abusing the noclip glitch. The boss is scaled well, considering every player can get over 650 max HP if they invested enough time into it.