Slayer Magic

Help I was wondering if I could get approved for a special type of third generation dragon slayer. I have come up with a unique lacrima Known as Dragon essence Lacrima basically is the implementation of heart, soul and Personality of a dragon into a lacrima which means that whoever implants one can utilize dragon slayer magic but also speak and learn through the dragon in the Lacrima. For my character he has the Dragon essence lacrima of the Umbral (darkness) dragon king Nocturne who through their journey together teaches him dragon slayer magic making Erebos a special type of dragon slayer. So I was wondering if I could use that idea and if anyone else wants to use is just ask

Are there any specific requirements I need to make a character who uses a type of Slayer Magic?

I was wondering if a person can have two different slayer magic abilities. Like could someone have Dragon Slayer Magic and then also have Devil Slayer Magic. I'm working on a fanfiction where the main character has Fire Devil Slayer Magic, and then a different element of Dragon Slayer Magic. But I wasn't sure if this is possible or not.

What are your Favorite Dual Element Modes?

Mine is:

Iron Shadow Dragon Slayer Magic

Poison Shadow Dragon Slayer Magic