Question

should there be a comma before the highlighted word?
after squidward tentacles built a water slide in his backyard we spent all our afternoons splashing around.

Explanation:

The sentence starts with a dependent adverbial clause ("After Squidward Tentacles built a water slide in his backyard") followed by an independent clause ("we spent all our afternoons splashing around"). When a dependent clause precedes an independent clause, a comma is required to separate them.

Answer:

Yes, a comma should be placed before the highlighted word "we". The corrected sentence is: After Squidward Tentacles built a water slide in his backyard, we spent all our afternoons splashing around.