Tributing a monster for "Mystik Wok" is a cost, so you can Tribute "The Legendary Fisherman" or "The Agent of Force - Mars".

The ATK or DEF is the current number, not the original number.

You select ATK or DEF when "Mystik Wok" is activated.

You can Tribute face-down monsters, or your opponent's monster using "Soul Exchange".

Cyber Blader: The opponent controls "Gemini Elf" and "Dark Magician". The opponent attacks with their "Dark Magician", attacking "Cyber Blader", whose ATK is currently doubled. The opponent activates "Mystik Wok" and Tributes their "Gemini Elf" to gain 1900 Life Points. "Cyber Blader" now has 2100 ATK points, so it does not destroy "Dark Magician", but since the opponent has only 1 monster now, "Cyber Blader" is not destroyed as a result of battle, either.

Peten the Dark Clown: If "Peten the Dark Clown" is Tributed for "Mystik Wok" or "Cannon Soldier", the last thing that happened was that those effects resolved, so the effect of "Peten" does not activate.