A level 5 grimer appeared?

Question

Gyarados used surf! (Used surf) In the castelia sewers A WILD LEVEL 5 GRIMER APPEARED.

Answer 1

Perfectly normal.
Whilst Surfing in Castelia Sewers, Grimer may appear at any level from 5 to 15.

http://bulbapedia.bulbagarden.net/wiki/Castelia_Sewers#Pok.C3.A9mon

Comments

I remember grimer appearing in a small lake in GSC, in Kanto, in front of a man who give TM softboiled in RBY

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yes you are right MiniNinetales