A dark mnemonic to help remember the ‘iru’ and ‘eru’ godan verb exceptions. Let me know if it helps!

I know (知る) who created the godan verb exceptions.

I go(参る) to his street and enter (入る) his house.

I put in (入れる) my knife and cut(切る) him.

His blood decreases (減る).

I run (走る) away.

Later I return(帰る) to the scene of the crime.