I play a spell with an Overload ability.
I sack the spell to Nivmagus Elemental
do I still get the Overload effect since the original spell has been exiled?
(I would have already payed the Overload cost.)
No. It is as Salla
wrote. The spell in exile does not resolve. An overloaded spell doesn't create any copies or anything like that. It is just one spell. If it was overloaded then it does different things if it were to resolve.
Also Nivmagus Elemental
exiles spells. It does not sacrifice them. Sacrifice has a specific meaning. For example Dragon Appeasement
cares when you sacrifice a creature and does not trigger if you were to use Food Chain
_Magic: The Gathering_ Comprehensive Rules
These rules are effective as of October 1, 2012.
702.94a Overload is a keyword that represents two static abilities: one that functions from any zone in which the spell with overload can be cast and another that functions while the card is on the stack. Overload [cost] means "You may choose to pay [cost] rather than pay this spell's mana cost" and "If you chose to pay this spell's overload cost, change its text by replacing all instances of the word 'target' with the word 'each.'" Using the overload ability follows the rules for paying alternative costs in rules 601.2b and 601.2e-g.
702.94b If a player chooses to pay the overload cost of a spell, that spell won't require any targets. It may affect objects that couldn't be chosen as legal targets if the spell were cast without its overload cost being paid.
702.94c Overload's second ability creates a text-changing effect. See rule 612, "Text-Changing Effects."
Rules Q&A would gain you the fastest response to a rules question.
November 17, 2012 11:00 PM PST
Overloading a spell does not create a new spell
it just modifies what the spell looks like
if you exile the spell none of its effects will happen, overloaded or otherwise
November 17, 2012 11:30 PM PST
What you're trying to do only works with mechanics that specifically copy the spell. See Precursor Golem
, storm cards
, and replicate cards