Goat format ruling
Mystic Swordsman LV6

Card effect (current official text)Cannot be Normal Summoned (but can be Normal Set). At the start of the Damage Step, if this card attacked a face-down Defense Position monster: Destroy that monster, and if you do, you can place it on top of your opponent's Deck instead of sending it to the Graveyard.
Rulings
- The Normal Summon (Tribute Summon) of this monster is the same as a Tribute Set. This card must be in face-down Defense Position when it is Normal Summoned (Tribute Summoned). If you Normal Summon (Tribute Summon) this monster, it is placed face-down on the field; you do not have to show your opponent what monster it is.
- If you activate the effect of Mystic Swordsman LV6 to place a face-down monster on top of your opponent’s Deck, you do not get to look at it.
- If Mystic Swordsman LV6 attacks a face-down monster, its effect activates at the beginning of the Damage Step, before the monster is flipped face-up. If Ceasefire was activated during the Battle Step to flip the monster face-up, then the effect of Mystic Swordsman LV6 is not activated. A monster destroyed by the effect of Mystic Swordsman LV6 is not destroyed by battle. There is no damage calculation. It is not flipped face-up. Any Flip Effects it has are not activated.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Goat forum — sourced change requests get reviewed.