While I've not read the author's fix up novel "The Voyage of the Space Beagle" (aka "Mission:Interplanetary"), I've read 3 of its 4 original short stories (all 3 are online). This post is about the original short stories that were later woven into the novel.
"Black Destroyer" is one of the most famous monster stories of the genre, & among the best known of the author.
- "Black Destroyer" (A); download; Astounding, July 1939: A practically immortal super-being of an alien world is attacking human visitors & threatens to overrun inhabited galaxy.
- "Discord in Scarlet"; Astounding, December 1939: Not read.
- "M33 in Andromeda" (B); download scans as part of a larger package; Astounding, July 1943: A group of human adventurers overcome a galaxy-sized monster!
- "War of Nerves" (B); download scans as part of a larger package; Other Worlds, May 1950: Cultures reach an inferior stage during their evolution, & then forever stay there!