Scummy Pendu Analysis is a legendary drop from a Scummy Pendu. You may have to kill them for a while until this material is found due to legendary bring the rarest tier in the game—it's represented by the color Orange. Scummy Pendu Analysis, when exchanged with Mizuhagawa Environment B, can get you one of the best gifts to give to Tsugumi.
These flying Others can be found in the Kikuchiba—Upper-Level Construction site, or Kunad Highway—Suoh Exit.
In Kikuchiba, you can encounter Scummy Pendu's as soon as you enter, but to get to the second group, you need to use SAS Teleportation from Luka to pass the fence that blocks entry. But in the second area, you have to kill many others after you kill the Scummy Pendu.
For Kunad Highway, you'll encounter them not long after you appear in the area and then another group not long after, which makes the Kunad Highway the best place to farm for Scummy Pendu Analysis.
Scummy Pendu has a low health pool, so killing them is not an issue. To get them to respawn, teleport to another area that is not in Kunad Highway. Then teleport back to the Suoh Exit, kill them and rinse and repeat!
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