Okay so lets talk about this card !
First of all it works well with
Black Kyurem EX which is able to tank itself up to 300 hp ! It would be quite difficult to target down and KO such a Pokemon with 300 hp which is dealing 200 damage a turn with energy acceleration such as Blastoise which was reviewed in last weeks card of the week !
However a Black Kyurem-EX is hard to kill already with 200 hp, so does it really need the extra 100 hp ?
The idea of Black Kyurem-EX is to one hit knock out an opponent's EX Pokemon which will net you 2 prizes and it is difficult to revenge KO this Pokemon already if it has no damage on it. Firstly it has 200 hp which is enough to tank a fair amount of damage and it has weakness to dragon which is not seeing as much play unless you count itself being it's own weakness.
Dragons are not used commonly as counter Pokemon and more as offensive attackers.
Also the downside to this card is that it is an ACE-SPEC trainer which means you cannot use ACE SPEC cards such as Computer Search, Scramble Switch,Gold Potion,Dowsing Machine or even Victory Piece.
Here is a list of the current ACE SPEC Trainers available:
https://bulbapedia.bulbagarden.net/wiki/Ace_Spec
Computer Search and Scramble Switch are probably the 2 best ACE-SPEC trainer cards in this current format (Plasma Storm on-wards.) Giving an EX Pokemon an extra 100 HP doesn't sound as good as being able to search your deck for any 1 card or move a damaged Pokemon out of the active position with a fresh set of energy ready to attack !
Tool Scrapper can counter this card by removing the tool off of the Pokemon, so once you play it, it is committed to the field.
These ACE-SPEC trainers are more universal and allow you to use them in any deck whilst Crystal Wall is only available to use in decks which are playing Black Kyurem-EX.
You can even catch your opponent off guard with a well timed Gold potion which is probably better as it can't be countered.
So the summary:
Playability: 2/10
Artwork: 4/10
I can't give the artwork much credit as it literally is just a trainer card with a very mediocre picture. If this card was not holofoil the artwork would be 2/10.
The card is playable if you don't have any ACE-SPEC trainers and are using a Black Kyurem-EX in your deck but if you're not then this trainer card is virtually useless to you. I would swap this card out for a Dowsing Machine,Computer Search or Scramble Switch when one becomes available to you.