Silverfur Partisan + Zada, Hedron Grinderor or
Mirrorwing DragonI had a big discussion about this ability recently and I thought It may be useful to post this for people who say the combo doesn't work.
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Copying a spell also copies all decisions made while casting it, including targets, number of targets, distribution of damage or counters, the use of an alternate cost, and a couple other things. The copy effect will tell you exactly what changes, if any, are being made to those copies. Most spell-copying effects let you choose new targets, but
Zada, Hedron Grinder's effect specifically tells you what the new targets are. Also, there are currently no copy effects in the game that will allow the number of targets of a spell to be changed.
"Becomes the target of" means first it wasn't a target, and now it is. Because
Silverfur Partisan's ability doesn't care about whether the instant or sorcery was cast, the copies made by Zada will trigger it.
Compare this to the Heroic ability, in which casting does matter (and won't trigger for a copy made by Zada):
Hero of Iroas, etc.
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Hope this helps for anyone else who was confused on this combo when it came out:)