The secret to Ending A being revealed so late in the game is downright diabolical. Brilliantly done, you monster. Definitely not replaying for that. Great work, this was damn fun, and just the right level of frustrating.
Edit
SPOILERS BELOW (why doesn't itch have a spoiler censor option?)
I was wondering how it would work, so I just tested out an Ending A attempt. I grabbed the double jump then immediately jumped into the spikes to see if I would retain the powerup upon respawn. Instead I find myself back at the main menu. I repeat: DIABOLICAL.