[...] Instead, can't we have something that promotes Trios?
That. It'd be a 'dream-come-true'..
Lots of good ideas here. (
http://elementscommunity.org/forum/index.php/topic,25097.0.html) In particular, this idea is one of the most balanced and intresting solutions. (
http://elementscommunity.org/forum/index.php/topic,25665.html)
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Anyway, it seems to me that those who are supporting the concept of Shards are those who like the idea of a serie of other cards that are able to provide some benefit to every element, while being particularly useful for their own element. However, I see it this way.
If shards are overpowered, when compared to in-element cards, then that aim is not reached, as the shards themselves will become the center of the competitive decks, whether they are based or even use the proper element, or not. For instance, death has nothing to do with Shard of Sacrifice's power when used in SPlat, nor in ToaST. One other example is Shard of Focus as of now, or Shard of Gratitude before the nerf. Those cards are not adding to the game, they are taking away from it.
If shards are underpowered, they are not going to be used. Shroedinger's Cat-like cards are not adding to the metagame, and Shard of Patience is a brilliant example of that. Take away Shard of Sacrifice and you'll have the same problem with Shard of Divinity, most likely. These cards are not helping towards that aim too, since they will not be beneficial to even a single element (not even their "intended" one). See how even Fracsalia is not enhanced by Shard of Patience.
If shards are useful with their intended element, but not useful at all without it, then they might as well be cards of that element. That way, they are not rainbow friendly. If shards are useful outside their element and stronger inside it, then you have very powerful cards that benefit every element and are rainbow friendly. That means those cards are either too powerful in their element or too powerful in rainbows.
The "likable" shards are somehow strong yet balanced in their own element, and useful but not overpowered in other elements and rainbows. I should note that this situation is painstrikingly difficult to reach from a balance point of view.
Now, how is that different from using cards from another element in rainbows, duos or trios? For rainbows everybody will probably agree that it'd be a lot more balanced. For monos, you will be able to use balanced cards (they ARE balanced in their own element, aren't they?) at the cost of changing around the quanta balance and being slightly less reliable (therefore, you won't be able to use them quite as effectively). And for duos? You'd be forced to use a trio, thus being a lot less reliable and effective. But instead of going for that terrible goal of the perfect balance between all factors, wouldn't the game benefit more if you just added 12 elemental cards and a card to quanta-balance trios (
http://elementscommunity.org/forum/index.php/topic,25665.html)? You'd be having the same effect as your aim implies AND gain SIX HUNDRED AND SIXTY trios (seriously, 660 new deck types in one go!). How is THAT worse?