Prison code: 2605
Talk to the four prisoners in order. Their highlighted numbers form 2, 6, 0 and 5. Entering that sequence unlocks access to the first key; the code is a room puzzle, not a redeemable reward code.
Recover before the castle fights
A healing pad is near the Sentient Statue corridor after the spiral stairs. Another is near the throne-room entrance. Use the appropriate pad before triggering each encounter instead of arriving with resources spent on the rooms before it.
Story king versus optional rematch
Cruel King is the Chapter 1 finale that leads to Ice Dagger. Returning after the chapter and Shedletsky dialogue opens Blackrock King / Cruel King DX, whose Last Stand and Famine mechanics need a different plan.