This page tells you how to defeat all the Bosses in Undertale ... an eye on her sprite. Or alternatively, the answers are: D, C, B, D, A, D, anything, C, and A. Once the battle is over Mettaton ...

Asriel Dreemurr is the true final boss of Undertale, coming after you've explored ... so pick them appropriately to keep yourself alive as the battle progresses - dying isn't terminal in this ...