I have searched Gatherer and forums for a more detailed explanation (with no luck) of why because I don't understand it.
I would have calculated it as follows.
Fencing Ace when attacking alone with no enchantments will deal two damage (as it is a 1/1 creature with double strike). In the combat phase it will deal damage together with creatures that have first strike and deal 1 damage. As it has double strike it will deal 1 damage again when normal creatures deal damage in that combat.
When it is enchanted with 3 x Ethereal Armor and the 3x Ethereal Armor cards are the only enchantments in play I would say that as the owner of Fencing Ace has 3 enchantments and therefore Fencing Ace is now a 1/1 creature with +3/+3. Therefore I thought that when it attacked with these enchantments it would do 4 damage at the stage when creatures do first strike and then do 4 damage again in the normal damage step as it has double strike, dealing a total of 8.
Although Ethereal Armor says it gives first strike, I understand that this does nothing in this case as Fencing Ace already has double strike.
I must be missing something basic but I don't know what... Thanks
Ethereal armour gives +1/+1 for each enchantment you control. You control 3 enchantments (assuming the ethereal armours are the only enchantments you control) so each gives +3/+3. This gives the ace a total of +9/+9, making him a 10/10.
During each combat step, he deals 10 damage for a total of 20 damage.
Is there a specific part of this you don't understand?
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