I think the PG is just like incomplete in the rating of rarity.
Common
Uncommon
Rare
Extremely Rare
Extremely Extra Rare
A scale of 7~8 ratings would be much cooler.
or something like this try :
0- S ( stock, more than 25 Neostore copies ) - Sengoku 3, KOF2K1
1- VC ( Very Common ) - Magician Lords, Nam1975...
2- C ( common ) - Football Frenzy, Ghost Pilots...
3- U ( uncommon ) - Sidekicks 2, Karnovs Revenge
4- HTF ( hard-to-find ) - Viewpoint, Last Resort...
5- AR ( aspiring rare ) - Galaxy fight, Sengoku 2...
6- R ( rare ) - Savage Reign, RBFF ...
7 ER ( extremely rare ) - Metal Slug 2, Ninja Masters, NTM ...
8 UR ( unbelivable/Ultra Rare ) Ultimate 11, Kizuna Encounter
What ya think ?
