So.. You roll a number of dice equal to your skill.
You KEEP a number of dice equal to your stat.

How do you determine success or failure? What does 'keep' mean in this context?

Other than that: What is the reason for calling your system 'Mortal?' Is it that the game is very punishing, that it's very easy for characters to die? Or is it very heavy combat focussed with lots of blood, gore and death?

It's indeed a very hard task of coming up with a name for a game system. Especially if it's the system you need a name for; settings are easy.

Ask yourself what you want to accomplish with your system. What are you trying to create that you find lacking in other systems? Why are you making the system in the first place? Where do other systems fall short? The answers to those questions should help you create a name for your own system.