Your sentence is almost perfect! Here’s the original:
They call me a killer whale. I am that scary!
Explanation:
- The sentence is grammatically correct and clear.
- "They call me a killer whale." is a correct simple sentence.
- "I am that scary!" means you are really scary, and it sounds fine as an informal expression.
If you want, you could also say "They call me a killer whale because I am that scary!" to connect the two ideas in one sentence, but your original is great as it is!