At common blue gets Mocking Sprite, which provides a handy Goblin Electromancer effect
Finding those cards can be a challenge so I recommend looking at actual decks you want to play and see what win-cons those include
While Sram, Senior Edificer is also good draw, its only off of cast, and so should always be second choice to Puresteel
This human cleric generally works best on your turn so you have the best chance of using that mana, though black has plenty of 2-mana removal spells to fire off at instant speed
But despite the power here it's not my top option from the set
Getting around pesky indestructible effects, whilst also helping you along if you have anything at all that cares about people sacrificing their stuff, its not difficult to see why this colorless sorcery made it so far up the list