Xbooru - 2010s 2016 2boys 2d 2d (artwork) animated skeleton bigger male biting lip black and white black hair blue jacket bottom sans clothed digital media (artwork) ectotongue fellatio genitals hair over one eye hand on another's head hand on head heart humanoid humanoid robot jacket ladybumtickler larger male licking licking penis line art lineart male male/male male only mettasans mettaton mettaton ex monochrome monster oral penis robot robot humanoid sans sans (undertale) seme mettaton sex size difference skeleton smaller male sniggysmut third-party source top mettaton tumblr username uke sans undead undertale undertale (series) video game character video games white background yaoi