It was heavily rumored that, by saying things like "Sony", "Playstation" or even "Sega" into the microphone, you could get Pikachu to become mad. However, it appears that this is in fact an urban legend, as there is no indication in the data file that these words were supposed to be registered. The few registered cases of an Angry Pikachu were probably just caused by the game not understanding what was said, which in turn led it to just pick a random word similar to what was heard.

Right outside the sliding glass door of the player's room are a pair of shoes in the Japanese version which are nonexistent in the English version. In Japan, people take their shoes off before entering their homes, a tradition which America doesn't follow so strictly.

Every Pokémon except Pikachu, Caterpie, and Butterfree have different cries between the two versions due to English names that differ from the Japanese names.

The Nintendo 64 in the Japanese version looks rather unpolished and appears to have Super Famicom cartridges with it, which doesn't make sense since N64 cartridges are the same in design between America and Japan and Super Famicom games can be played when the Tristar 64 is attached but nothing seems to be attached.

In the US release, going to Cobalt Coast in Pikachu's Play Days leads to a Piñata party where Pikachu has to hit a Pokéball Piñata. In the Japanese release, Pikachu instead plays a similar game called Suikawari.

The objective of the game is to hit a watermelon with a stick, with Pikachu wearing Ash's hat from the anime series to cover his eyes. There are watermelons scattered around along with bananas. Pikachu can trip on the watermelons a couple times before he has to quit the game, whereas tripping on bananas is an automatic game over.

If Pikachu loses, he gets a Soda Can Tab in the Japanese release, and a bottle cap ring in the US release's "Pokéball Piñata".

The Japanese version has eggplants, whereas the US version has corn. The result is that Japan misses out on popcorn which is obtained when Pikachu shocks the corn.

In the Japanese version of the game, Pikachu can play with an Onigiri (Riceball). In the US version, this was changed to a Cupcake.

At E3 2004, a tech-demo for the Nintendo DS featuring Pikachu was playable and was made to show off the DS' capabilities. It featured microphone mechanics very similar to Hey You, Pikachu! as well as some additional features.