The main playable character of the 2015 RPG "Undertale" is a monster.

The answer is false because the main playable character of the 2015 RPG Undertale is not a monster, but rather a human child named Frisk. Throughout the game, Frisk falls into the Underground, a world inhabited by monsters, but they themselves are not a monster. The player controls Frisk as they navigate their way through various encounters and decisions with monsters, determining the outcome of the game based on their choices.