I've been blending D&D and Gamma World since 1980. I can confirm much awesomeness.
But beyond that, I customize monsters to settings. This is even more fun than just adding random abilities, because even though a minotaur is a minotaur from a stats perspective, it's different if the setting has minotaurs as civilized vs. bestial vs. divine creatures.
When creating your next setting, take each monster, examine it and decide HOW, WHERE, and WHY it exists in your setting. Don't be afraid of being creative.