2 card ideas like Shatterpillar and Cocoon tend to do only as well as (or worse than) the First card in the absence of the second in the poll system. There is also the theory that the game would be better off with Fireflys (which would be suggested first and upon acceptance by Zanz a Firefly Queen could be suggested) than with Malignant Cells (token second cards presented with the first.)
Actually, I didn't thought this idea as two cards but as the two states of one creature (similarily as burrowed/unburrowed devourer). I made the two cards to explain how it would behave in game. Anyway, I didn't submit this idea to the crucible because it is still a rough idea. It is part of a brainstorming I've started here: Opposing elements duos as soft PC (
http://elementscommunity.org/forum/index.php/topic,27050.0.html). I might use any of the community suggestion to transform this later into a totally different card. So, don't hesitate to comment and make suggestions.
Caterpillar seems strange in that neither Life nor Death has any means for Hard PC. 
is enough to kill a creature but not IMO to destroy a permanent. Also it is very complicated as I mentioned before.
I agree it is difficult to find a theme fitting life or dead which would explain the destruction of a artifact. However, I do not think that it does not exist. For example, you can see that nature (e.g. forest) can eat back a complete city or swallow a building. Here I tried to illustrate the use of something dead (namely an object/artefact) to make something alive (a cocoon) which would be used to promote the growth of a creature (the whole phenomenon being similar to building a nest).
