More than 25 Trainer cards and a new Special Energy card
Explosive Getaway Explosive Getaway might not cut it for the most cutthroat of Cubes, but a 5-mana wrath that handles most small to mid-sized threats while protecting your best card seems pretty sick at the right power level, especially since you get another enters trigger out of the deal
The only downside is that your turn ends immediately after
Space-Time Smackdown offers only two viable tools: Rocky Helmet and Giant Cape, with the latter being the more competitive option
The way most Izzet decks look in my cube, from aggro all the way to control, is pretty spell heavy, and often containing more artifacts than your average cube deck
The cards might read well, but they could (and in some cases do) lead to awful play patterns and unfun experiences