Thank you for playing and for beating my challenge! I appreciate the kind words! :D
To answer your confusion, Boss's stats are determined by the sum of the ORIGINAL stats of their materials (if a card is boosted or assisted by another, and used for a Boss summon, the boss will not retain the boost nor the assist), and when a Boss loses a life, its material with the highest stat amount gets removed (a boss made with two cards with 500/1/500 and a 400/0/400 will lose the first one if it would be defeated).
Aaand I see you noticed Azriel...well...he is one of the strongest cards of the game and honorary Boss killer for sure, it actually gave me balancing problems from its first inception😅 (fun fact: when I first made the prototype on paper and played with my friends, I had to literally make a banlist only to limit him to 1 card per deck).