For a Bitcoin novel reader contest, formats that stay fair without becoming a pure hash-power race:

1. Multi-stage with a public oracle — each stage publishes a checksum/address so solvers verify locally (BIP39→BIP84 oracles work well). Avoid “5 missing seed words” unless positions are fixed; that space explodes past the prize.
2. In-text riddles whose answer is a short passphrase to a brainwallet or BIP39 entropy (MD5/SHA256 of an exact string). Document encoding rules (whitespace, case) so there is one canonical hash.
3. Time-released clues across chapters rather than one giant final keyspace. Readers who finish get a real advantage over brute force.
4. Escrow on a fresh address you control, with a published sweep deadline so unclaimed prizes return to you.

Happy to expand on oracle design or BIP path choices if useful.