My first 3-0 Izzet draft. A tempo shell can work after all. It reminds me of U/R in Dominaria where you play early creatures and bounce their stuff. I don't know why people are sleeping on Selective Snare; I've picked them up pretty late. Against Boros, you almost can't lose because almost everything they have is either Human or Soldier. Resetting their Mentor counters is so backbreaking. Electromancer combos quite well with it, letting you bounce and play another threat on the same turn. Fire Urchin is also pretty decent. Rarely do people want to trade it so you can get some early damage in. Mid/late game you can tap/bounce their creatures or play Cosmotronic Wave for the kill. It also combos well with Wojek Bodyguard. Both are big enough to not die from Direct Current or Righteous Blow too.
Some notes:
1. Direct Current is by far the best common, maybe even uncommon. A lot of times you need to get rid of a creature on t3 which Beacon Bolt doesn't allow. Beacon Bolt is still very good though. You can easily set up turns to get rid of a x/3 or a x/4 creature especially with an Electromancer out. Then you can do it again the next turn. I'd rate them both higher than Hypothesizzle. As nice as drawing cards is, you don't want to have too many five drops.
2. Wojek Bodyguard is your second best common three mana spell, possibly even better than Hypothesizzle. You want to preserve your creatures as much as you can, which the bodyguard does by adding counters on your two drops. If they want to kill the two drop, that's perfectly fine. If they kill the bodyguard, it's still usually mana parity. If they Luminous Bond or Capture Sphere it, you can bounce it back at a later time. The worst removal spell against it is probably Dead Weight, making it a 1/1 and turning off Mentor. I compared it to Ember Beast in the past, but it's actually way better.
3. I think I'd rate Fresh-Faced Recruit the highest among two drops. I don't know why Kenji thinks the Ornery Goblin is better. It fights 1/3s better, but it still trades with 2/2s. They're both soft to Cosmotronic Wave. Mentoring the recruit is so much better than mentoring the goblin though. The goblin will still die to 2/2s whereas the recruit can just keep attacking. I think even Fire Urchin is better than Ornery Goblin in Izzet. Electromancer usually wheels and you don't want to have too many of them because of diminishing returns. A 2/2 also doesn't fight particularly well. League Guildmage is fine but not much better than Electromancer. Beamsplitter Mage is too narrow. Vedalken Mesmerist is playable.
4. Barging Sergeant is really good. A lot of removal spells are sorceries, so it's very easy to just hit for 7+ damage because most decks want to race. If they kill it the next turn, you still got value and damage out of it. If they play a creature, you can Sonic Assault or Hypothesizzle on your turn. You don't want to trade the sergeant unless it's absolutely necessary. That's why you don't want too many Hypothesizzles. I think 1-2 is the right amount depending on how many Barging Sergeants and Watcher of the Mists you have.
5. Cosmotronic Wave shines against Selesnya, but don't play too many of them; 1-2 is fine. It's still worse than Direct Current, Beacon Bolt and Hypothesizzle. Selective Snare is more flexible so I'd rate it higher.
6. Invert // Invent is fine if you have a lot of Muse Drakes; you can pump them to 3/1. There are also a few defenders you can kill and 1/4s you can ambush with a Fresh-Faced Recruit. I'd only play it if you have spells that can close the game with Invent though. I played a variety of instants and sorceries that I could fetch. If you don't I would not play it.
7. Piston-Fist Cyclops is probably bad in this deck. You'd need to play things like Maximize Altitude/Velocity to trigger it consistently. Wee Dragonauts is the better spells payoff.
8. Three Guildgates is probably too much. I think 1-2 is the right amount. More is fine if you have Crackling Drake or ol' Nivvy obviously. Play more mountains if you can't divide by 2 because of Direct Current's double red cost. 17 lands is the correct amount because of Jump-Start.
9. I had Ionize in my sideboard, but it was mostly clunky even with Electromancer out. Sonic Assault is better in most matchups I think.