Here's a question: with Expert Water Magic, during a battle for a castle, if my Archons go first, and I cast Clone on them and then use Wait, will the Clone go next?
And my second question: do skills and artifacts that grant resistance work on the Clone?

If the opponent has a creature with the same speed, then after the Wait action, the opponent will go. All resistance skills and artifacts work on the Clone. It would be strange if they didn't. Just make sure that after casting (for example, Armageddon), the original survives, because if the original dies, the Clone will disappear.

Added 4 minutes later

Please explain this rule point and how it works:
Comments on 2.13. Bugs.
The use of bugs considered "features" of the game is allowed:
- weakening unupgraded neutral armies through repeated defeats;

If you attack 70 Cyclops with an upgraded stack (7 stacks of 10), and then lose or retreat, the unit will decrease by the size of the upgraded stack, i.e., there will be 60 of them. Repeat. Profit! This is the so-called multi-defeat bug. It seems to have been fixed in HD+, but I might be wrong. You can use this bug in online games.