For the purposes of the Professor Pine research papers and the fan fiction, we will be using Smogon's tiering system, albeit slightly altered.
AG - Class S+
Uber - Class S
OU / BL - Class A
UU / BL2 - Class B
RU / BL3 - Class C
NU / BL4 - Class D
PU - Class E
Little Cup - Unclassed