You can unlock it in Builder’s Workshop (Arena 6)
High damage but slow recharging.
Best use for him is as high damage backup troop placed behind a meatshield like Golem, Giant or Lava Hound.
Don’t waste Sparky ‘s damage on low hitpoint units. Make sure to put other troops to cleare the way for Sparky.
How to counter this card? You can use Zap and Freeze spells. They can stop and reset Sparky’s charge. Also you can use Fireball or Rockets! Skeleton army is good to!
Use Minion Horde or other flying troops.