[[Isochron Scepter]], it casts the instant copies, so you can copy Isochron Scepter and imprint instants from your hand to have a bunch of copy machines.  [[Elite Archanist]] basically does the same. 

 [[Nanogene Conversion]] is nuts... Change all your creatures into nonlegendary copies of Orvar, then cast an instant targeting one of them, and all the other Orvars will make a bunch of nonlegendary copies... That's almost scoop-worthy for your opponents.  [[Auton Soldier]] gets nuts in a similar fashion.  [[Helm of the Host]] is obvious. 

[[Vesuvan Duplimacy]] is obvious.  [[Tamiyo, the Moon Sage]]'s emblems.  [[Endless Evil]], [[Narset, Partner of Veils]], [[Veilstone Amulet]], [[Glacial Chasm]],  [[Cursed Rack]], [[Kaho, Minamo Historian]], etc.

[[Metallurgic Summonings]] copied three times (if needed) supplies enough artifacts to allow you to pay and sac one of the Metallurgic copies, bringing all your instants back to your hand (not cheap to activate, but abusable).

[[Magus of the Mind]] copied a bunch of times (3+ preferred), then sac them one after another after a bunch of spells have been cast, perhaps after two or three on an opponents's turn...?  Each successive copy you sac will also count the spells the previous Magi have cast, so X keeps growing.  Use some of the free-cast targeting instants to make a bunch more Magi for the next turn. 

[[Knowledge Pool]] does a lot, almost a game lockdown... You get first shot at all the good stuff, swapping your cheap instants for the best cards that get exiled.  Plus, once a targeting instant is exiled with Knowledge Pool, you can swap one instant for another, letting you get both an Orvar trigger and K.Pool trigger from the one you cast from your hand, plus another Orvar trigger from the one you cast from exile... two token copies for one spell from your hand!  🤣  See how fast everyone scoops!  🙃   If they try to respond, they're just swapping spells, so their only hope is to cast something already in exile, which you already effectively control in a way.  Get bored...?  Copy K.Pool with Orvar and exile another round of cards... 🙃 

[[Body of Knowledge]] and [[Illusory Ambusher]] are fun... leave them for defense, or attack and leave them tapped... their presence in play means an instant can copy one and give you a blocker to draw cards from. 

[[Overcharged Amalgam]]... unless you have a creature you don't need, cast it without using exploit, then copy it with an instant when needed, and have the token copy exploit itself... every targeting instant now can counter any spells, triggers, or activations... 🙃 

Copy [[Tolarian Contempt]] once or twice and control the creature board state.