The Blob That Ate Everyone by R.L. Stine (Goosebumps)

A famous horror writer. That’s what Zackie Beauchamp wants to be. He’s writing a story about a giant blob monster. A pink, slimy creature who eats up an entire town! Then Zackie finds a typewriter in a burned-down antiques store. He takes it home and starts typing. But there’s something really odd about that typewriter. Something really dangerous. Because now every terrifying word Zackie writes is starting to come true.