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|Avg. deck rating||15.14|
|Favorite formats||Commander / EDH|
|Last activity||3 days|
From the Gatherer
"7/1/2013: If the exiled card is a split card, then X is the sum of the converted mana costs of each half. However, when you cast the copy, you choose only one half to cast. You may cast a different half each time you create and cast a copy."
And regarding the Fuse mechanic, you can only Fuse a split card if you cast it from your hand.
Lightning Strike will still resolve. Aurelia's Fury's effect doesn't affect spells that were already cast by the player.
Yes, you can deal damage to a planeswalker with it. Any burn that can target a player can be redirected to a planeswalker that player controls. If damage is dealt with Aurelia's Fury to a planeswalker, that player can still activate an ability of that planeswalker if he or she hasn't already done so that turn.