It is better to attack with a Dark Magician and have a spell/trap card which destroys a card on the field than having the card and Dark Magician Knight in the deck.
I don't think so. It being a special summon frow the graveyard means the monster that this card summons has a double use. You can mill, discard, fuse with it etc before you summon it.
Dunno in DL, but in other YGO games, Arkana's DM is somewhat treated as separate card since it has a different passcode than Yugi's DM, despite having the same name. Perhaps that's why.
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