Rule 34 Dev - 2010s 2018 2boys 2d against_the_wall against_wall animated_skeleton blue_penis blue_scarf boots commission_art ectopenis fallen9choirs fellswap fellswap_sans gay humanoid male male/male male_only male_penetrated male_penetrating male_penetrating_male penetration sans sans_au sanscest scarf scarf_pull sex skeleton tagme underfell underswap underswap_sans undertail undertale_(series) undertale_au yaoi|5703708208