At the very least, it seems like there's leeway for a DM to rule either way on tunnel-creation via burrowing.
If it doesn't advance HD, the psicrystal rapidly becomes a stronger monster, I think.
At the very least, it seems like there's leeway for a DM to rule either way on tunnel-creation via burrowing.
If it doesn't advance HD, the psicrystal rapidly becomes a stronger monster, I think.