"Subterror Guru" and "Subterror Fiendess" in the Damage Step

[kevinlul]

Situation: Guru attacks or is attacked, opposing player activates an effect before damage calculation that is negated by Fiendess.

Correct behaviour:

• if Guru is attacking, it is immediately flipped back up to DEF and the battle ends

Q.
Your "Subteller's Guru" attacks with the "Giganber Niche of the Amaryllis" equipped with the opponent's "Mirror of the Moon".
Chain the effect of "Moon Mirror Shield" and activate the effect of "1" of your "Sub Teller's demon" targeting that "Sub Teller's Guru".
What happens to that battle and damage in this situation?
A.
In the case of a question, "Subteller's Guru" becomes a backside defense display due to the effect of "Subteller's demon", and becomes a front side defense display after a series of processing.
At that time, the attacking "Subteller's Guru" is in defensive display, so damage calculation is not performed, and as a result, they will not be damaged.

• if Guru is being attacked, it is immediately flipped back up to DEF and the battle proceeds normally
  From rulings for Gemini Counter

Q: My opponent activates "Forbidden Scripture" when calculating damage in a battle in which my field's dual monster is the target of an attack.
Chained this card and activated this card, the attack target dual monster was displayed on the back side defense, and the activation was disabled.
The monster that was the target of the attack when the damage was calculated is displayed on the back side of the defense. What will happen to the battle after this?
A: Damage is calculated by setting the attacked monster to face-up defense display. (16/03/18)

Neither of these happens at present. Puzzle

Originally reported 19/02/2020 by Naim, rulings collected by pyrQ