June 25, 2012
One of the levels in McPixel has the titular character in a castle similar to the ones from Super Mario Bros., specifically on the bridge where Bowser is fought, and there are a character looking roughly like Mario while one looking like Raphael from Teenage Mutant Ninja Turtles, only with spikes on his back, replaces Bowser. There also are some mushrooms on the ground, referencing the Super Mushrooms from Super Mario Bros., also having the same color pattern.
If the mushroom is given to Mario, he will transform in a weird form and defeat Raphael, so a cutscene will show of Mario meeting a character wearing a mushroom hat, referencing the Mushroom Retainer from Super Mario Bros.
The creators of McPixel held no right over Mario and Teenage Mutant Ninja Turtles, but they only included minor references to the two series.