Bosses
Boss order, cards, and rewards
Order the tables agree on
There is no separate boss-rush mode in the sources. Rematches are real: Joan, Death, and Isaac each appear twice, and only one of those appearances drops a card. Dracula is two phases at the end. Counting 13 boss cards plus the fights that drop nothing is how the '13' and '18' numbers can both be true.
A practical order is The Fallen (800), The Warrior (1,800), The Prophetess (1,500), Saint Louis (12,000, Valmanway), Death's story fight (20,000, no card), Isaac's phantom (1,500, no card), Carmilla (4,500), Talos (5,000), Brauner (4,250), Mammon (8,000), Arthur (11,000), the Temptress (8,000), Joan's rematch (11,431, Courage, no card), the Doppelganger (8,778), Death in the Choir (8,444), Isaac at the clock (2,500), then Dracula (7,666) and the beast phase.
How to read a boss page
Each fight page has the room, the health, the reward, and the pattern notes that a named source actually printed. Attack timings I do not have are omitted. The Prophetess page is the character and the key. The Medusa page is the same fight's patterns, so you do not need both for the win.
What I ran into
I lined the Fextralife health column up with the IGN guardian pages before I trusted a number. Where only one table had a health value, the boss page says which one. I did not average them.
Castlevania: Belmont’s Curse Gameplay and Commentary Trailer
Questions
Is there a boss rush?
No mode by that name shows up in the sources. Joan, Death, and Isaac can be fought again as story rematches.
How many bosses are there?
Thirteen boss cards, plus story fights that do not drop a card, plus Dracula's second phase. Map tools count 18 boss markers.