This is the second Training Grounds combo and another potential turn 3 win. The combo consists of Izzet Guildmage, Training Grounds and Manamorphose. You need 3 mana up to go off with a minimum of 1 red and 1 blue. How it works is that you cast Manamorphose using the RX mana holding priority (hold down ctrl while casting in MTGO) and copy it with the guildmage using the blue. Now let the copy resolve and choose UU, use them to copy the original spell twice, let the copies resolve for UUUU, copy the OG spell 4 times and so on until you have enough mana and draw enough cards to find a Lighting bolt. Then let enough of your copies of Manamorphose resolve and have the last one you resolve make UR so you have mana to copy a lethal number of lightning bolts. Cast lightning bolt holding priority and copy it as many times as needed.
It's good to keep the original Manamorphose unresolved on the stack and some extra blue up in case your opponent counters the lightning bolt (which, in case you've stacked up a number of mage triggers removes their target spell and fizzles all of them), then you can either respond by copying Manamorphose again a number of times, either to dig for/cast a Izzet charm to counter the counterspell or to just find another lightning bolt and copy a lethal number on top of the counterspell. All this happens at instant speed so you can hold the combo up and go off in response to a removal spell if you think your opponent has one.
The ideal opening is Turn 1 Training Grounds, Turn 2 Izzet Guildmage, Turn 3 Manamorphose and go off for the win.
Izzet Guildmage + Training Grounds can obviously also be used to copy other spells directly just as a value/utility play without going infinite.
