I dislike this soft counter idea, there are a lot of cards this wouldn't even help against.
Maybe allow you to pick one of these mark upgrades?
I like a lot of these ideas much better than the idea as listed. A few suggestions, though...
Cast Heal for free.*
Or how about healing 3 every turn. So it's the equivalent of having a Shard of Gratitude if you have a mark other than
.
Airborne status is removed from all creatures.**
I think that's too specific in what it would counter. As
has a lot of effects based around the health of the creatures on its side of the field, how about all your creatures gain 0/+2. In other words, making an unupped Otyugh into an upped one.
Airborne creatures cannot be targeted by your opponent.**
Probably OP. How about gaining 25% chance they cannot be targeted, stackable with Shard of Freedom. In other words, have this and play 3 Shards and you'll have the 100%.
Opponent starts with 2 poison counters.**
Or, to make it stronger, every creature your opponent plays has a chance to die instantly (like a preemptive Skull Shield).
Draw 2 cards.*
Or, perhaps,
creatures don't suffer from the summoning sickness.
Begin the game with a +2 purify counter.**
Or, for something a little more powerful, all creatures your opponent plays have a chance to enter the game frozen.
Heal 10 whenever your opponent draws an extra card.**
Your creatures ignore shields.**
The heal seems like a
ability, and the shields seems like
. How about any creature of yours which is killed has a chance to not die, Shrodinger's Cat-style?
I really like your ideas, although I'm less keen on the idea of having one-off effects which can be triggered. Something passive for each element would be much better, I think.