I usually do not like playing with the Spark Pixies, but as it is the card for this weekly battle challenge let’s review it.

Tactical advice

I usually avoid the Spark Pixies because of its low life level. That makes it vulnerable to cards with the « opportunity » ability. And this is quite hard to protect against. You can easily protect your long range unit from « sneak » & « snipe » by placing long range units with a lot of life at the start and end of your long range line (cards like the Ettin Speaman, and the Prismatic Energy are perfect for it).
But how can you protect against units with « opportunity » ? There is only one way, which is to put expendable units with low life counts before the one you want to protect. You can for example place a Furious Ckicken or Creeping Ooze in front of the Spark Pixies to protect it. But it means you are consuming lot of monster slots for nothing, that might deserve it only if the game has low mana cap. And even so you would put cards in profession the Spark Pixies won’t last long, if your enemy summons some monster with opportunity…

When to use the Spark Pixies ?

Back to basics is for me the only safe setting to use the Spark Pixies. Without fear of opportunist you can place it the end of your firing line and enjoy it nice double damage.
Fog of war setting will also make it slyly less vulnerable. But the risk of opportunist remains.
Armored up will make the cards reasonably more resilient. But pay attention if the earth splinter is available: the basis earth summoner will cancel the extra armor.
Eathquake is a reasonable setting to get your Spark Pixies out, as it is flying.
Close Range setting will make the card a bit more interesting (like every other long range cards)
Even Stevens & Little League setting will encourage you to play with the Spark Pixies but don’t give you any tactical advantage to do so.

When to avoid the Spark Pixies ?

Reverse Speed & Aim True settings are to avoid at all cost. Indeed those setting will make you lose the main advantage of this card : the ability to ditch some attacks (high speed and flying ability).
Target practice setting could also be a risk

battle example

Here is an example of battle which was justifying the use of the Spark Pixies
Mana cap: 27
Setting: Back to basics & Small League
As I mentioned back to basic is the best setting for this card, as it avoid the risk of opportunist.
Small League constraint made of Spark Pixies the strongest unit I had at hand.
Below is the lineup I used :

In a back to basics setup I generally use only one melee units as without special abilities only the front unit can attack. Then I’m placing my available magical units and then the long range one. This allows maximizing the attack power by only having active unit. Magic units are obviously placed before the long range one to increase the time during with long range units are firing.
I was able to defeat the enemy army…

… with acceptable casualty rate :