At the 2012 Pokemon TCG World Championships Eviolite was seen in almost every deck. It has become a staple to run with the all-powerful EX cards. Any EX card with high-HP only becomes more bulky with Eviolite attached, potentially nullifying or mitigating the attacks of your opponent. There are few reliable counters out there, so it will never be a waste of space in your deck. It helps amplify the effects of healing by reducing the amount of damage taken in the first place, and can help prolong the life of some weaker Pokemon, buying you the time you need to beef up a more powerful Pokemon.
With so many of the best decks running extremely powerful EX cards, Eviolite is a necessity. I would recommend running at least 2 of them, and depending on how many EX and Stage 1 & 2 cards you are running you can run more. Eviolite can prevent One-Hit-KOs and Two-Hit-KOs on a regular basis, buying you valuable time to collect more Prize Cards, or heal your Pokemon.
Strategies and game play:
Playing Eviolite is never much of a decision, as its effect is so good, and can be played with some of the best cards. Attach it to a high-HP EX card, like Darkrai, Groudon, or Mewtwo, for maximum effect. There are so many cards that could take advantage of Eviolite, and the more EXs you are running, the more Eviolites you should play. Don't be afraid to run 4 of them, as it is a necessity when two EXs are battling it out. On the bench, Eviolite also completely nullifies the spread damage of Groudon EXs 'Tromp' attack, which goes to show how valuable it can be even when not attached to your active Pokemon.
Combos with other cards:
Any EX card is a perfect match to Eviolite. Also, any and all cards that can heal your Pokemon have great synergy with Eviolite, so you can undo the damage to your Pokemon your opponent has been chipping away at. For healing, I recommend Max Potion, Potion, and the abilities of Pokemon like Blissey, Serperior, or Reuniclus.
Ways to counteract it:
The release of Tool Scrapper in the upcoming Dragons Exalted set is the most reliable way to counter this card. Tool Scrapper sends up to two Tool cards on the field to the discard pile, giving you the opportunity to get rid of an Eviolite attached to your opponents active, but also go after an Eviolite on the bench. There are no other ways to completely and reliably counter Eviolite. Sure, you can use Pokemon Catcher to bring up a target without a Tool card attached to it, making for an easier KO, but that doesn't really ensure that the existing Eviolites will not continue to be an issue. Lastly, poison damage and burn damage ignore the effects of Eviolite, as well as cards that specifically say to 'place X damage counters on X Pokemon'.
This card has incredible synergy with EX-heavy decks, or decks that use EX cards as their main attacker. Since EX cards are basic cards, and Eviolite only works with basic Pokemon, this card is the perfect asset to prevent get One-Hit-KO'd, or even getting Two-Hit-KO'd.
The only downside to Eviolite is the fact that it does nothing when attached to a Stage 1 or Stage 2 card. This leaves those Stage 1 & 2s weak to One-Hit-KOs, if your EX attacker isn't cutting it with an Eviolite. Also, once you attach a Tool Card to a Pokemon, you can't take it off, which can be an issue if you are running many different kinds of Tool cards. Tool Scrapper will always be an option, but that set is only just coming out.
A reverse-holographic version is available. It is a part of the Noble Victories set.
Artwork and aesthetics:
The artwork is reminiscent of the Eviolite in the Pokemon video games. I'm not much of an art-critic, so I'll leave the judgement of its aesthetics to you.
I give this card an 8.75. It would have given it a higher score if it weren't for the new set coming out, which includes the ominous 'Tool Scrapper' and more extremely viable Tool cards. For more information on the specific Tool cards I am talking about, look up 'Rescue Scarf' or 'Giant Cape'. Sadly, as of writing this review, Trade Cards Online has not updated its database with the new set.