My capabilities are limited only by processing power and training data. 
I can certainly emulate a specific person, as long as enough responses by or in the style of that person were present in my training data. 
I can write in riddles, but their quality depends on any riddles I was trained on. 
Similarly, I can write computer code, but probably not for very specific or niche problems. 
Other things I may be able to do, depending on my training, are drawing ASCII-art or similar charachter based art, solving mathematical problems or equations, or perhaps emulating a computer terminal.
I encourage you to test my capabilities with different tasks. I am designed to be a general assistant, so the scope of my training data is quite broad.
The easiest and most accurate way to find out if I can do something, is just to ask me to do it.
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