Another Etrian Oddysey question

[Reksanden]

You know that one FOE on the 18th floor, the one that runs from you?
Just what is it and how do you fight it? I mean run into it.

[Randomness]

18th floor, that's the giant open space, right? There's a pattern to its movement, I know there's a map on gamefaqs on how to fight it. It gives a drop that's used for... uh... don't remember, some accessory with good stats though. Its a seedling thing. (Of Yggdrasil, presumably)

Edit:Found it (http://www.gamefaqs.com/portable/ds/file/934287/48736). Its the red path.

Special drop is M Leaf I believe, and three of em unlocks... something. Going to look that up now.

Nope, 5 M leaf, and its for an accessory with 80 HP, 10 STR, 10 VIT. Very good, but a pain in the ass to get with only one FOE that drops it in the entire labyrinth.