Final Submission
Undermine
It's a drill Pokemon, so it's associated with mining and drilling into the ground. It also prevents secondary moves from being used, so it undermines them. The name also fits its dark characteristics.
To me, this is by far the best suggested name as it is more than just a corruption of narwhal
How about the name Whalletus? The first half of the name ("Whal") obviously refers to our narwhal here while the second part ("lletus") is an anagram of the word Tellus, a Roman word meaning Earth. This refers to the Ground typing of CAP9 as well as to its Dark typing (Tellus --> Terra --> sub-terranean --> a dark place). So, "A Narwhal of the Earth", basically!
Other than that, I feel the name goes easy on the mouth and is fitting for CAP9. All suggestions are welcome.
Kujorlas (ku-djor-las)
(like in the word "job")
Kuro (means Dark in Japanese) - Jord (means Earth in Norwegian) - Valas (means Whale in Finnish)
Also, Kujo- sounds similar to "good job!" or "G'job", which refers to the fact that he stops the secondary, and does a good job at it.