The description from these forums and the wiki says:
Level 2: +25% base damage. Costs 16 AP.
Level 3: Destroys more tiles. Costs 17 AP.
Level 4: +25% base damage. Costs 18 AP.
Level 5: Damages all enemies. Costs 19 AP.
This matches what I see/remember as the in-game description for increasing power level.
I notice at L2, the pattern looks like this:
oxxxo
xoxox
xoxox
xoxox
oxxxo
But it looks the same at L3. Pucco’s post in the Character Discussion thread indicates that the pattern is larger at L4. Am I missing something, or is the description incorrect?