Nitrome included a high resolution image of Gunbrick in the skin as a hint of the mobile version of Gunbrick, as they thought the game would have been finished around the time of the skin's release, though unfortunately this was not the case. 
↑Comment by Frostyflytrap: I see that you hinted the new Gunbrick look in the Kraken skin, sneaky eh. ;)
Game Developer's Blog - Nitrome:
And the secret game is... → comment by Nitrome: Yeah we thought the game would be finished sooner so we put a hint in the skin which we have done lots of times for upcoming games., 21 Nov 14, retrieved 22 Nov 14.