It's not bad for what it is.
I like the anticipation you build by recreating the final scene in Undertale. And then by interrupting it with the burning Switch logo and characters, it brings prominence to the fact that it's a new experience coming to the Switch-- like it's going to be a *whole* new experience. As if it's not the same game anymore.
I think you did well with the animation and theme. You took Undertale's release to the Switch and made it feel like it's going to be something unique.
Not too shabby. It almost fills me with determination (to buy the game a second time.)
The only thing that's lacking is extra content beyond what you've already animated-- maybe interaction between Undertale and Nintendo characters-- maybe the rest of the gang of Undertale showing up to see what the big deal is about the flaming logo. Either way, it's a good promo.