We must beware of monos in all of our battles.
Darkness, I predict, will come with some kind of voodoo deck. I would suggest taking quints, but we have none so it's moot point.
In any case, I highly suggest we not go mono this round. Losing a bunch of earth cards, even if we only lose as few as one, is going to hurt in the future. We should avoid taking advantage of the event card this round for this reason, as well as another:
Most teams will attempt to take advantage of the event card, and go mono. If we go 7-0 this round, we will be able to salvage 42 cards. 90% of which will most likely be off-element cards (compared to a 60-75% without the event card) this will severely bork our vault with off-element cards that we most likely won't use for anything besides converting. And we won't be doing that much converting.
I suggest that we only take advantage of the event card this round if we are confident that we will not face a mono.