I'd like to know all the ways to auto-crit. The only ways I know are through the paralyzed and unconscious conditions, and the Assassin rogue's Assassinate ability.

The only ways I know to impose the paralyzed condition is through the spells *hold person* and *hold monster*; and the unconscious condition through the spells *sleep*, *eyebite* L7 (can cause sleep), and *symbol* L6 (can cause sleep).
And, possibly the *command* spell to cause sleep for 1 turn if the DM allows it.

So for doing this somewhat reliably and not being over level 10, boils down to *sleep*, and *hold person*/*hold monster*.

What's the comprehensive list of ways to auto-crit in D&D 5e?