I like this idea. I think burrow would be more thematic, but if you do have Hiding Place, it should cost 3
![Earth :earth](https://elementscommunity.org/forum/Smileys/solosmileys/../../../images/Misc/earth18x18.png)
, be a one-time use (can have more than one on your field, but requires 2 or more spirits) and make all spirits immaterial while it is on the field.