The Slug Buddy in "The Way of the Sponge" appears to be red in color. In "Squid Defense," it is now mainly brown in color and it appears to be bigger in size as well. The words "Slug Buddy" are also written near the top.
"The Great Snail Race"
The Slug Buddy is first used as a punching bag by Gary punching it with his eyes.
"The Way of the Sponge"
The Slug Buddy is used by SpongeBob when he is training hoping to impress Fuzzy Acorns. The Slug Buddy ends up knocking SpongeBob away however.
The Slug Buddy is used mainly by SpongeBob and Sandy to help train Squidward for karate. At first, Squidward doesn't even budge the Slug Buddy but later, manages to knock it away.
Between the two episodes, the Slug Buddy has appeared at SpongeBob's House and Sandy's Treedome. It is unknown if SpongeBob moved the Slug Buddy to Sandy's place or they both have different Slug Buddys.