Of course, it takes three different Xyz monsters to make, so it had to be worth it
Yes, the white cards that draw you cards when your opponent casts spells cover the full range of only use in special cases to format staple. The best such card is Esper Sentinel, which requires opponents to pay mana to cast noncreature spells or you'll draw you a card
Unbeknownst to Kaiba, Yugi's card was actually a mirror
Commander play is more likely, possibly even in the command zone, but there are a lot of better, easier-to-cast options out there
The corner is angle-cut on top material to assist insertion of cards and prevent card corner damage.
(2017-08-25) If a creature has been dealt damage, that damage remains marked on it until the cleanup step