A few questions, on timing, and changing efx

[serracollector]

1. If I cast frantic search, tapping out to do so, which happens first the untap, or the discard, or at same time? Reason I am asking, if I have a madness card in hand, can I untap the lands, then cast it, etc, or is it discarded before I can untap the lands to pay for its madness cost?

2. If magus of the moon or blood moon is in play, Great Furnace becomes a mountain, but is it an artifact still, for purposes of say metal craft, or to sac to tinker/shrap blast/atog etc.?

ty

[Clariax]

1. You carry out the instructions of the card in the order they are printed.  However, the madness triggered ability will not go on the stack until the Frantic Search is completely done resolving, and you don't actually cast and pay for the madness spell until that triggered ability resolves.

2. Magus of the Moon and Blood Moon both affect the land subtype of the land, they do not affect the types or supertypes in any way.  An artifact land is still an artifact, a legendary land is still legendary, etc.

[serracollector]

Ty.  And for another question, since it is an artifact, if I have blood moon/magus out, and Null Rod, can it still tap for red as a mountain, or is it "completely" shut off by Rod since its still an artifact?

[Wagner]

As all artifact lands and other mana producing artifacts, it will be shut down.

Null Rod doesn't care what the card originally did, if it's an artifact, it cannot be activated.