Creative, has lots of interesting synergies (overdrive, gravity pull, flood...)
One "exploit" is that this could be paired up with basilisk's blood to transform 2
into 25
, this would take 6 turns though (does the sponge continue picking up HP naturally while it's delayed?). It could pair with plate armor to turn 1
into 7
(3 plate armor HP + 2 initial HP + 3 HP for the turn needed to get rid of summoning sickness), or with heavy armor to turn 1
into 10
. Water -- the new "immo" rush?
Why is sponge free? Even without basilisk's blood or plate armor, this thing generates quanta 2 or 3 times faster than a pillar! Of course, you have to sacrifice it to get that quanta, but still...
Finally, the upped version shouldn't have the HP+1 while also having the numbers themselves changed. No point making it overly complicated, and the upped version is already much more powerful than unupped even without the HP+1 part.