Katress – Abyssal Sorcerer

With an ability that states "Choose up to X cards," can I choose 0 cards?

Yes, you can. Even if there are eligible cards to choose, by choosing 0 cards, you can effectively choose not to select any.

I have multiple copies of the same card with a [Once Per Turn] ability in my base. Can the [Once Per Turn] ability be activated once for each individual card?

Yes, it can be activated. For example, if you have multiple copies of TD01-008 〈Stone Pit〉 in your base, even if you activate the 【ACT】 ability of 〈Stone Pit〉 A, you can still activate the 【ACT】 ability of 〈Stone Pit〉 B.

What is 〈Butcher〉?

It means putting the specified number of Pals in the Base into the graveyard. For 〈Choose 1 of your Pals, and butcher it〉, choose 1 Pal in your Base and put it into the graveyard.

I have a copy of BP01-074 《Shadowbeak – Seed of Despair》 in the rest state and BP01-075 《Katress – Abyssal Sorcerer》 in my base, and no effect other than 《Shadowbeak – Seed of Despair》 is causing it to be night. If 《Shadowbeak – Seed of Despair》 is butchered in this state, how many times does the 【AUTO】 ability of 《Katress – Abyssal Sorcerer》 activate?

It activates twice.

I have a copy of BP01-074 《Shadowbeak – Seed of Despair》 in the rest state and BP01-075 《Katress – Abyssal Sorcerer》 in my base, and no effect other than 《Shadowbeak – Seed of Despair》 is causing it to be night. In this state, 《Shadowbeak – Seed of Despair》 was butchered by its own 【AUTO】 ability at the end of the turn. In this case, how many times does each 【AUTO】 ability activate, and in what order should they be resolved?

First, at the end of the turn, the 【AUTO】 ability of 《Shadowbeak – Seed of Despair》 activates twice and enters a pending state. By resolving one of the pending 【AUTO】 abilities of 《Shadowbeak – Seed of Despair》 and butchering 《Shadowbeak – Seed of Despair》, the 【AUTO】 ability of 《Katress – Abyssal Sorcerer》 activates twice (factoring in the 【CONT】 ability of 《Shadowbeak – Seed of Despair》) and enters a pending state. After the resolution of the first 【AUTO】 ability of 《Shadowbeak – Seed of Despair》, you can resolve the remaining one 【AUTO】 ability of 《Shadowbeak – Seed of Despair》 and the two 【AUTO】 abilities of 《Katress – Abyssal Sorcerer》 in any order.

I played a card that states 〈Choose up to X (specific) cards from your graveyard and return them to your hand〉 or 〈Choose up to X (specific) cards from your graveyard and deploy them〉. What happens if there are no such specific cards in the graveyard?

Choose 0 cards and resolve the rest of the effect.

If BP01-075 《Katress – Abyssal Sorcerer》 is butchered, does the 【AUTO】 ability of the butchered 《Katress – Abyssal Sorcerer》 itself activate?

Yes, it activates. Even if 《Katress – Abyssal Sorcerer》 itself is butchered, its own ability activates, allowing you to deploy a Pal with a cost of [its cost - 1] from the graveyard.

While BP01-075 《Katress – Abyssal Sorcerer》 was in my base, I butchered a ◇5 Pal. Can I deploy a ◇2 or ◇3 Pal using the 【AUTO】 ability of 《Katress – Abyssal Sorcerer》?

No, you cannot. You can deploy a Pal with a cost of [its cost - 1]. In this specific case, you can only deploy a ◇4 Pal.

While BP01-075 《Katress – Abyssal Sorcerer》 was in my base, I activated the 【ACT】 ability of BP01-093 《Meat Cleaver》 and butchered one of my 5-cost Pals. The 【AUTO】 ability of 《Katress – Abyssal Sorcerer》 triggers; should I resolve this or the ability of 《Meat Cleaver》 that states 〈Reveal the top 3 cards of your deck, choose 1 card from among them and add it to hand, and put the remaining cards into the graveyard〉 first?

Resolve the effect of 《Meat Cleaver》 first. Even if an 【AUTO】 ability activates in the middle of resolving an effect, the pending 【AUTO】 ability will be processed after the resolution of the current effect finishes. In this case, after the effect of 《Meat Cleaver》 finishes resolving, you can choose a Pal with a cost of [butchered card's cost - 1] from the graveyard to deploy with the 【AUTO】 ability of 《Katress – Abyssal Sorcerer》. As a supplementary note, if a Pal with a cost of [butchered card's cost - 1] is among the cards put into the graveyard by the effect of 《Meat Cleaver》, it can be chosen by the 【AUTO】 ability of 《Katress – Abyssal Sorcerer》.