3 Level 4 monsters
Once per turn, you can activate 1 of these effects.
* Detach 3 Xyz Materials from this card; destroy all other face-up monsters on the field.
* Detach 5 Xyz Materials from this card; destroy all cards your opponent controls.
So, Thunder Spark Dragon needs 3 Level 4 materials to be summoned, with a somewhat lacking 2400 ATK. His first ability allows you to Dark Hole, except himself, at the cost of 3 of his Materials. His second ability lets you Short Circuit at the cost of 5 of his materials - waitwut, he only has 3?! Yes, friends, this card is the only Xyz monster that doesn't begin with enough Materials to use its effect. But, we'll get to that in a minute.
Summoning Thunder Spark Dragon is fairly easy, since he has no extra requirements. Getting him out can be easily accomplished using fellow REDU monsters Mahunder and Pahunder in tandem with another Level 4 like Thunder King Rai-Oh or Wattgiraffe. Apart from Thunder decks, you can utilize 2 Summoner Monks to summon another and an additional Level 4 monster and Xyz. Decks like Madolches and Gadgets can swarm using Ultimate Offering to pull out Number 91. There are a lot of other ways to get him out, but these are just a few.
Thunder Spark's first effect is easily used. It's Dark Hole, plain and simple, but you still have a monster with Monarch power. Since you've likely exhausted your monster repertoire getting Spark Dragon out, you probably won't have any monsters to risk being destroyed anyhow. Still, you can always take advantage of Spark's effect to build up a contingency plan by allowing your Sangan to be destroyed to grab a Tour Guide from the Underworld.
The second effect of Thunder Spark is somewhat tougher to pull off. Being able to zap the opponent's entire field is nice, but you have to somehow acquire 2 more Xyz materials to attach to him. Only 4 cards in the entire game will put Materials on him: Spirit Converter, Overlay Regen, Overlay Eater, and Xyz Unit. So, which card is best?
* Spirit Converter: This card works wonders in a "hunder" deck, since you'll be able to easily garner LIGHT monsters to attach to Thunder Spark Dragon, and can take advantage of the secondary ability of Converter and refuel your hand. This card is also the most direct form of adding materials to Thunder Spark, since it can be reused each turn to add a Material; this ensures you'll have Number 91 up and running within two turns.
* Overlay Regen: Regen is very good at what it does in a simple way, just making itself an Xyz Material. This one is good for simplicity.
* Overlay Eater: Eater steals your opponent's materials to add to Thunder Spark. The thing is, you need to have Eater in the Graveyard and your opponent needs an Xyz Monster, while you have Spark up. So, Eater isn't a very good choice.
* Xyz Unit: This card is essentially Overlay Regen with the added bonus of boosting its equip's ATK. Of course, it can be hit by Mystical Space Typhoon.
So, the best choice is... anything besides Overlay Eater. Really, you can go with any of the other three. Converter closes your deck options down a bit, so it's somewhat specific. Regen and Unit have their own niches, whereas Unit will give Thunder Spark a decent 800 boost if you don't use the effect, but Regen will not get hit by MST (which, if your opponent expects their field to get blown up, they will activate).
Number 91: Thunder Spark Dragon has a lot of flaws besides its need for Materials. Simply dropping Effect Veiler, or flipping Fiendish Chain/Forbidden Chalice will not only negate his effect but he will have 0 materials, making it hard to replace. His ATK is also pretty lackluster, since a Number 17: Leviathan Dragon or Numebr 39: Utopia can up and kill him on the turn after he's summoned.
Usability: 3/10, really, I see no reason to use him over Number 16: Shock Master, since that card is less costly and keeps you safe for up to 3 turns.
Art: 9/10, very cool looking, with an appropriate electric blue color scheme worthy of its name. Serpent-like dragons are always nice.
Next week's theme will be covering the upcoming TCG releases from the Return of the Duelist Special Edition, Legendary Collection 3, and the 2012 Wave 2 tins.