SSE Mod that Makes Serana do a Bite Finisher

[Dubbadizzo]

I'm looking to make a mod that makes Serana have a 15% chance to finish off those in combat with a bite animation IF the attacker is both under 25% health and a living humanoid (Human, Argonian, Orc, Elf, Khajit).

I'm new to modding so I have no idea where to begin and tutorials on something like this are few and far between.

I figure I start with an EventOnhit or an EventCombatStart, and I also figure this is a script you could place on Serana in CK, but again I really have no idea how or where to start. Help!

Thanks in advance.