I've really enjoyed the deckbuilding for phase 2 for the challengers. At first I was unphased at the 33% in-element restrictions, but was wondering how difficult the "twice per Bo5" for off-element matches would be to work around.
Then I started deckbuilding. I came up with some ideas and tried to make them into decks, but for every deck I made there seemed to be two ideas that I couldn't bend into only having ten off-element cards for. Being a Life challenger, this was particularly challenging as Life has very few splashable cards to fill a deck with. I began cursing how difficult this was and was thinking how much I would love a few more off-element cards.
Slowly, as I started making more extra decks I realised that I was being pushed to my limits in Life. I would have to work out every nook and cranny I possibly could to keep my decks fresh and relevant for my opponents. Since then I've really enjoyed working with these limits, and I'd say they're quite suitable for the Trials.
The biggest downside to these rules have been the unfortunately large number of illegal decks played, which has left me with an extra, hollow, victory. The limit to the number of times an in-element card can be played appears to be the biggest problem. While I can understand that it's there to prevent one element abusing a card which is a weakness of their opponent, it looks like many people have found it too easy to forget that they included a specific in two of their previous matches.