E1 Unlimited has been pretty well documented, but here are a couple things that immediately come to mind when I hear “obscure”
• 025/BW-P through 031/BW-P Promos that were never officially handed out due to the 2011 earthquake
• Prototype Gen 1 Birds that we got more info about thanks to Akabane a couple years ago
• PTFG Groundbreakers “unreleased” cards that are floating around
• L2, L3, and WCP Unlimited print runs, albeit a very large number have popped up in the last 5 years after not knowing much about them prior
• DPt-P Promo versions of Darkrai and Cresselia that PFM was lucky enough to snag