Big Shield Gardna

Edison Card Text
If this 1 face-down monster is targeted by a Spell Card, negate that card's activation and change this card to face-up Defense Position. If this card is attacked, change it to Attack Position at the end of the Damage Step.
Duelist League 2010 participation cards • 2009-08-15
No targeting
No Damage Step effect
Banlist • Unlimited
Interactions
Does Big Shield Gardna have an effect while face-down?!
Big Shield Gardna is set face-down and targeted for battle.
Yes. It is an exception and can apply its effect while face-down.
Rulings
edisonformat.net
●A face-down Big Shield Gardna can only negate a Spell Card that targets 1 face-down monster, so it can't negate Riryoku, Creature Swap or Dark Hole, but could negate Nobleman of Crossout or Tribute to the Doomed.
●If Big Shield Gardna is targeted with a Spell Card, you may chain Book of Moon to flip it face-down, then it can negate the Spell Card and will flip back to face-up Defense Position.
●Skill Drain only negates the effects of monsters that are face-up on the field, so a face-down Big Shield Gardna may still negate a Spell Card that targets it while Skill Drain is active on the field. It will still be flipped to face-up Defense Position, and now its effect that changes its battle position when it is attacked will be negated.
●If Prickle Fairy attacks a face-down Big Shield Gardna both their effects will occur at the end of the Damage Step. Prickle Fairy will be Step 1 and Big Shield Gardna Step 2. So it will change to Attack Position, and then the effect of Prickle Fairy will change it back to Defense Position.
edisonformat.com
A face-down "Big Shield Gardna" can only negate a Spell Card that targets 1 face-down monster, so it cannot negate "Riryoku", "Creature Swap" or "Dark Hole", but could negate "Nobleman of Crossout" or "Tribute to the Doomed".
If "Big Shield Gardna" is targeted with a Spell Card, you may chain "Book of Moon" to flip it face-down, then it can negate the Spell Card and will flip back to face-up Defense Position.
"Skill Drain" only negates the effects of monsters that are face-up on the field, so a face-down "Big Shield Gardna" may still negate a Spell Card that targets it while "Skill Drain" is active on the field. It will still be flipped to face-up Defense Position, and now its effect that changes its battle position when it is attacked will be negated.
If "Prickle Fairy" attacks a face-down "Big Shield Gardna" both their effects will occur at the end of the Damage Step. "Prickle Fairy" will be Step 1 and "Big Shield Gardna" Step 2. So it will change to Attack Position, and then the effect of "Prickle Fairy" will change it back to Defense Position.