=== Simple ===

Entering this room jump and whip the third candle, if you hit enough flea men/birds with the holy water (reminder hitting the bone dragon before the stage 12 door will ensure this) this candle will drop a double multiplier.

After collecting the double from the third candle you can do a quick pause buffer and this will put the bone dragon on the correct cycle to jump it.

Alternatively, you can jump up and collect the double, while falling do another delayed whip that should put the bone dragon on the correct cycle.

For both of these options proceed to the right, jumping the second bone dragon and onto the boss fight.