(noun) A wrinkly toad that lives in disgusting woman's vagina. If a penis penetrates a vagina inhabited by an undertoad, it is at risk of being bitten off, eaten, and/or savagely mauled. Most undertoad have rows of many razor-sharp teeth, the better to ravage upon your male genitalia and/or objects of pleasure.
Broman: ew, ugh, dude, that chick last night had an undertoad. almost got my dick bit off.
Undertale is a game created by indie developer, Toby Fox. In it, you can choose to either spare every entity that appears before you, or slaughter them mercilessly. It has multiple endings, a fantastic soundtrack, and although it doesn't have the best graphics, its story, wittiness, and humor make it a very enjoyable game.