The Nick Magazine Comics were strips made for Nick Magazine to promote the show. Confirmed by an e-mail from Doug TenNapel, there were a few 2-page Catscratch comics that were made for Nick Magazine.
The first one came out in the December / January 2005 issue. The second one came out in the March 2006 issue. The third and last one was in the February 2007 issue. As of now, we have located the first and second strips, the third one still remains a mystery.
1/3 - "New Ruler" Edit
This strip came from the December/January 2005 issue, before the show's premiere. In this one, a Space Slug lands it's ship onto a nearby field and demands to be the world's new ruler. In one of the later episodes in the show "Spindango Fundulation", a species of space slugs similar to the one displayed appear.
Tennapel.com Version Edit
Nick Magazine Version Edit
2/3 - "Off The Hook" Edit
This strip is from the March 2006 issue. In this one, the three brothers are shown enjoying a day of fishing, until everyone catches a fish except the superior Blik. On the 8th panel, popular Nickelodeon character Spongebob Squarepants can be seen on the bottom right.