The book is [*Science Fiction Terror Tales*](http://www.isfdb.org/cgi-bin/title.cgi?34236), a 1955 anthology edited by [Groff Conklin](https://en.wikipedia.org/wiki/Groff_Conklin). It has appeared under [several covers](http://www.isfdb.org/cgi-bin/titlecovers.cgi?34236); the one with the red cover is the [1969 Pocket Books edition](http://www.isfdb.org/cgi-bin/pl.cgi?257606): [![enter image description here][1]][1] [1]: https://i.sstatic.net/GZwBv.jpg The three stories you remember are "The Leech" by Robert Sheckley, "Arena" by Fredric Brown, and "Lost Memory" by Peter Phillips. **One about a blob that lands on Earth and absorbs matter exponentially. They launch it into space and blow it up, and now infinite pieces will land on more planets.** ["The Leech"](http://www.isfdb.org/cgi-bin/title.cgi?56294), a short story by [Robert Sheckley](https://en.wikipedia.org/wiki/Robert_Sheckley), available at [Project Gutenberg](http://www.gutenberg.org/ebooks/29525) and the [Internet Archive](https://archive.org/stream/Galaxy_v05n03_1952-12.Galaxy/Galaxy%20v05n03%20%281952-12.Galaxy%29#page/n107/mode/2up). > The leech was waiting for food. For millennia it had been drifting across the vast emptiness of space. Without consciousness, it had spent the countless centuries in the void between the stars. It was unaware when it finally reached a sun. Life-giving radiation flared around the hard, dry spore. Gravitation tugged at it. <br>A planet claimed it, with other stellar debris, and the leech fell, still dead-seeming within its tough spore case. <br>One speck of dust among many, the winds blew it around the Earth, played with it, and let it fall. <br>On the ground, it began to stir. Nourishment soaked in, permeating the spore case. It grew—and fed. **They launch it into space and blow it up, and now infinite pieces will land on more planets.** > It had been shrinking from the expenditure of energy, when the great explosion came. No thought of containing it. The leech's cells held for the barest fraction of a second, and then spontaneously overloaded. <br>The leech was smashed, broken up, destroyed. It was split into a thousand particles, and the particles were split a million times more. <br>The particles were thrown out on the wave front of the explosion, and they split further, spontaneously. <br>Into spores. <br>The spores closed into dry, hard, seemingly lifeless specks of dust, billions of them, scattered, drifting. Unconscious, they floated in the emptiness of space. <br>Billions of them, waiting to be fed. <br>**The second is about a human alien war where time freezes and there's a 1v1 duel in a sand pit with a barrier in the center. The alien is an armadillo type creature.** ["Arena"](http://www.isfdb.org/cgi-bin/title.cgi?41651), a novelette by [Fredric Brown](https://en.wikipedia.org/wiki/Fredric_Brown), first published in [*Astounding Science Fiction*, June 1944](http://www.isfdb.org/cgi-bin/pl.cgi?57540+c), available at the [Internet Archive](https://archive.org/stream/Astounding_v33n04_1944-06_AK#page/n69/mode/2up). A very famous story. From the [Wikipedia plot summary](https://en.wikipedia.org/wiki/Arena_(short_story)): > The mysterious Outsiders have skirmished with Earth's space colonies and starships. Their vessels are found to be faster and more maneuverable, but less well armed. There have been no survivors of the small raids on Earth forces so Earth has no information about the Outsiders. Fearing the worst, Earth builds a war fleet. Scouts report a large armada approaching the solar system. Earth's defenders go to meet them. All indications are that the two fleets are evenly matched. <br>Bob Carson is the pilot of a small one-man scout ship on the outskirts of the fleet. While engaging his Outsider counterpart in battle, he blacks out. When he awakens, he finds himself naked in a small enclosed, circular area about 250 yards (230 m) across. Other than vegetation and blue sand, he sees in the distance only a red sphere about 1 yard (0.91 m) in diameter. The sphere turns out to be an Outsider, with several dozen fully retractable thin tentacles to manipulate objects. Based on its method of movement, Carson labels it a "Roller".