The Platypus is one of the oddest mammals around-- they lay eggs, they don't have a stomach, but they do have a cloaca

 

From: https://environment.co/platypus-facts-that-are-stranger-than-fiction/

1. They Lay Eggs

2. Scientists Thought Platypuses Were a Hoax

3. They Don’t Have a True Stomach

4. They Glow Under a Blacklight

5. Males Are Venomous

6. Their Babies Are Called Puggles

7. Adults Have No Teeth

8. They Ooze Milk

9. They Can Detect Electrical Fields

10. They Have a Cloaca