Literally everything is countered by FEAR Rattata.
Ever since Endeavor existed as a move, and in fact made easier in Gen 4 when Focus Sashes were created as one time guaranteed survival.
Every legendary is countered by FEAR Rattata.
Steven is countered by six FEAR Rattatas.
Blue in FRLG onward is countered by six FEAR Rattatas.
Wallace is countered by six FEAR Rattatas.
Cynthia is countered by six FEAR Rattatas.
Lance is countered by six FEAR Rattatas.
N is countered by six FEAR Rattatas.
Alder is countered by six FEAR Rattatas.
Iris is countered by six FEAR Rattatas.
Diantha is countered by six FEAR Rattatas.
Kukui is countered by six FEAR Rattatas.
The other Title Defense NPCs are countered by six FEAR Rattatas.
Trace is countered by six FEAR Rattatas.
Rattata isn’t in SwSh or SV but if they were you bet your ass Leon, Geeta, Nemona, the AI Professor, and Kieran could all be beaten with FEAR Rattatas.