This scene is from the first chapter of the Yellow arc. Professor Oak is complaining about Red not bothering with the Pokédex because he wants it completed before all the Johto Pokémon turn up:
Now, the silhouette on the right is clearly a Donphan. But what is the thing on the left? It doesn't appear match anything that I can see.
Now, the silhouette on the right is clearly a Donphan. But what is the thing on the left? It doesn't appear match anything that I can see.