Stephen King’s “The Mist” has some similarities with Gravity Falls; according to wikipedia; the events of the “The Mist” were the result of a military experiment

“A military experiment performed in Shaymore, the “Arrowhead Project,” apparently intended to create a trans-dimensional window with which to peer through into other dimensions.”

And it resulted in tons of creatures from that world getting into our world and wreaking all kinds of havoc

The theme is not unfamiliar within sci-fi, horror, or Lovecraftian stories; but still interesting