You can also kill it yourself using spells, but in that case, it would be ideally a 6-7 mana, 2 cards combo to summon a 8 mana+ minion. Of course, Crazed Alchemist can combo it as early as turn 5 but that requires exactly these 2 cards by turn 5.
I decided to make it a 3 cost spell with Overload 2, as opposed to a 5 mana spell because this is the sort of thing that you want to use against aggro. It'll be a massive blowout against face hunter with all of their low health minions, so much so I'm starting to think the card might be a bit too strong. But then again, how many minions is the hunter going to have out on turn 3? 2-4 minions at the most and they probably won't all have 1 health. After that they could just Unleash the Hounds and clear your board anyway or play Explosive Trap and make the Dust Devils cry.
Anyway, the turn after this resolves it demands a response or you'll be taking tons of damage. Especially if they're holding onto Rockbiter Weapon or Flametongue Totem which made me lean back towards OP again. If you kill 5 minions and they don't have an answer for it then that's lethal right there... which isn't great fun for the other guy. Then again! Who has a board full of 5 1-health minions?
Other synergy includes a deadly follow-up to Imp-losion or Muster for Battle. Other than the uses it has for anti-aggro, the card becomes severely limited in what it can do (which is the same problem as Lightning Storm).
They should give you somewhere around 2/2,5 worth of stats, but you might miss out on the battlecry. However, some have some great upsides, like the Mechwarper or a Snowchugger. Of course you can get the worst outcome with the Explosive Sheep.
Atleast it's not weak to silence.
Edit: CHanged AGAIN due to some misunderstandings.