To add a few things:
The SoP do stack. However, the effect doesn't. If you manually remove it, the entire stack will be destroyed. Stacking SoP over the old one also removes the ability to destroy it that turn. So you must wait another turn to remove it. Thus, stacking SoP is capable but not recommended because of no positive aspect but many negative ones.
The attack increasing effect affects all creatures, including those frozen or already delayed. Newly infested cells will still attack for that turn only, since the delaying effect comes in before any of the creatures attack. It affects immortal creatures, including burrowed ones. With Adren, it acts normally, only delaying the first attack. In case of burrowed creatures, the bonus attack will be doubled upon unburrowing.
The price cost seems too low, though. Maybe 5
| 3
like typical shard cost would be enough?