Undertale OST...? - Gaster's Theme Extended

Undertale OST - It's Raining Somewhere Else Extended

Undertale Gaster Secrets

Undertale OST - Power of "NEO" (Full Version) Extended

Undertale OST - Undertale Extended

Relaxing Music (Instrumental) Romantic,Chill,Studying,Mind Refreshing

Undertale - Gaster & Deprived Gaster Fight (Fan-made)

Listening to All Undertale OST be like:

All W.D. Gaster encounters in Undertale

Undertale OST - Waterfall Extended

DELTARUNE OST - Rouxls Kaard Shop Hip Shop EXTENDED

relaxing undertale music by the fireplace + fireplace ambience

Undertale OST - CORE Extended

Undertale - Omega Flowey Boss Fight

Undertale OST - Spider Dance Extended

【undertaleAU】Last breath sans phase3 animation ～Last breath～

Game Theory: Who is W.D. Gaster? (Undertale)

Megalo Strike Back (Chara fight theme)

Undertale: The Hacker's End (VHS Sans) | Phases 1-3 (Corey's Take) | Full Battle Animation

Undertale Mashup - Hopes and Dreams - His Theme - SAVE the World - Last Goodbye

Undertale - No Hit Flowey (2 Segments)