This is the core of the copy series of decks.

It Needs:
4 Creatures
4 Instants
14 Lands
8 Sideboard Cards

Combos:

Blistercoil Weird + Retraction Helix: For every spell cast that turn return a nonland permanent to their controllers hand.

Elite Arcanist with Triton Tactics: By Making the Arcanist one of the targets of Triton Tactics you get 1 spell cast per mana.

Illusionist's Bracers + Elite Arcanist: This doubles the copy efficiency. Also gives extra spells for Nivmagus to consume.

Illusionist's Bracers + Strionic Resonator: Allows an extra copy of an activated ability.

Nivmagus + Illusionist's Bracers: 4 +1/+1 counters per spell consumed.

Elite Arcanist + Strionic Resonator: allows you to put 2 spells on the elite arcanist. You have to pay the sum of both spells, but can pick and choose the order.

One possiblity to keep in mind:
Cast some one drop(A)
Cast Swan song to counter A
Exile A with the Nivmagus
Result:
You pay 2 mana
Nivmagus gets 2 +1/+1 counters
You get a 2/2 flyer.

Things to keep in mind when filling out the rest of it.
Look for "Whenever you cast a spell ..." effects, even if you exile the spell(or copy of the spell) the effect will trigger.

Keep added spells a low mana cost to maximize spells cast per turn.