War Turtle is a Fighter Monster Room introduced in the Portable Power Expansion Pack. Backers of the Boss Monster 2 Kickstarter who opted for the Collector Box will get the Expansion early, while the Expansion will be on sale later on.
The color palette is meant to mimic the colors of the screen of a classic Game Boy.
Due to the Portable effect of this card, the underlying text can be activated every turn. The player can place the card back in their hand while it is in their dungeon, only to rebuild it again, thus activating the ability of the card. This card works well with rooms that have a "cycling" effect.
The man riding on the turtle looks like the early versions of Mario, while the spiked turtle would more than likely allude to being Bowser. The man looks like Mario during his days in the circus, such as during the Game & Watch Game, Donkey Kong Circus.
The man riding the turtle could also be a Kappa, an amphibious demon from japanese folklore.