Original Raw and Uncut
Two-Headed Starfish
I just don't get how one season could just have five different art styles? And the thing is I look at the credits, and they have about the same storyboard and animation directors. The main example is in season 2, witch has the most art styles
Style 1:

Used In:
Your Shoes Untied
Squid's Day Off
Bubble Buddy
Patty Hype
Christmas Who?
Style 2:

Used In:
Something Smells
Wormy
Grandma's Kisses
Squidville
The Smoking Peanut
Prehibernation Week
Squirrel Jokes
Mermaidman and BarnacleBoy III
Gary Takes A Bath
Frankendoodle
Jellyfish Hunter
Style 3:

Used In:
Bossy Boots
Big Pink Loser
Imitation Krabs
Life Of Crime
Dumped
Pressure
Shangied
Welcome To The Chum Bucket
I'm With Stupid
The Fry Cook Games
Sandy, SpongeBob, and The Worm
Style 4:

Used In:
Grayevard Shift
Krusty Love
Sailor Mouth
Artist Unknown
Style 1:
Used In:
Your Shoes Untied
Squid's Day Off
Bubble Buddy
Patty Hype
Christmas Who?
Style 2:
Used In:
Something Smells
Wormy
Grandma's Kisses
Squidville
The Smoking Peanut
Prehibernation Week
Squirrel Jokes
Mermaidman and BarnacleBoy III
Gary Takes A Bath
Frankendoodle
Jellyfish Hunter
Style 3:
Used In:
Bossy Boots
Big Pink Loser
Imitation Krabs
Life Of Crime
Dumped
Pressure
Shangied
Welcome To The Chum Bucket
I'm With Stupid
The Fry Cook Games
Sandy, SpongeBob, and The Worm
Style 4:
Used In:
Grayevard Shift
Krusty Love
Sailor Mouth
Artist Unknown