If you make sure you remove all of your opponent's creatures, the first time it enters, you are scoring a 5 life hit for 4 mana
You can cast Splicers Skill over and over with any spare mana, and Golden Guardian can become a golem factory with little effort
Lets look at some of my favorites and some hidden gems from the common and uncommon slots
Getting it at the time of your choosing, in order to save your creature during combat, from a direct damage spell, or to kill an opponent with an unblocked creature is gravy on the train
Flash and instant are not the same, but they function the same way
You can also pull them off to space yourself from some damage, although in a 40-life format I find I do that rarely