Cost: Destroy half of the Micromajigs you control (round up).
Effect: This turn, Micromajigs you control cannot be destroyed.
Flavor: "There isn't enough for all..."
Here I wanted to expand on the Hidden Sandwich idea and also make Micromajigs a little more playable competitively (since they are so easy to wipe out with almost any mass removal, and newer sets have introduced more mass removal).
I like the idea, but I think it would need another wording. And be able to work with cards other than Micromajigs, since it will come up in limited games.
cost: Pick a number for X. Destroy X characters. Pick X characters.
effect: This turn, the picked characters can only be destroyed by costs, and all inflicted to the picked characters is reduced to 0. At the start of your opponent's next turn. Destroy the picked characters.
I added the last sentence to make sure that it wouldn't get too exploited by other characters. Even though I'm not totally sure it wouldn't.
Yeah, I think your suggestion for the effect is better. It makes it more versatile while not making it overpowered and it is still probably best used with Micromajigs... ^_^