Best way to get the achievement is in "Samurai Shodown V". Not the Special or Perfect Edition.
Just play the game with a character you like, till you reach the final boss Gaoh.
To choose a new character, I decided to get wrecked by Gaoh.
The poor guy needs some motivation here and there.



Poppy, Galford's loyal companion, is a hidden, playable character. We have to enter a certain button combination. Just like in the good old days.

In the character select screen, highlight Galford. Don't press any button, just highlight him.
He is the blonde wannabe ninja...



Now push the following buttons:
Right, left, right, left, left, right, right, left, left, right, A

If it works, Poppy will appear.



Now show Gaoh who's the boss, with this cute little doggy, and you will earn the achievement.

Every Dog Has Its Day

Have Fun.