I like the idea behind the hero. For a healer though, she only has one direct healing ability. Pool's increasing/decreasing atk speed doesn't seem to be fit for this type of char to me, for some reason. Seems it would be too easy for the enemy heroes to simply walk out of it, unless you have some type of stunner around, of which there don't seem to be many so far in LoL (sure there will be more later). Still, maybe have it slow them a very small amount? Say 10% MS?
Perhaps even instead have Pool be a heal. Obviously it couldn't be for any large amount at all. Maybe .75/1.50/2.25/3/3.75 a second? Perhaps have each AP increase the heal by something like .20 HP/sec?
To enemies maybe have it reduce their HP regen/armor for an incremental amount?
I don't know enough about armor in the game to come up with an accurate number atm. Armor seems to run significantly higher than in DotA, maybe -5/-10/-15/-20 respectively, with AP increasing the amount by some number (Again, I don't know enough to come up with a number)
For the heal, though: Let's say the game time is at 20 minutes and you haven't died yet (A very unlikely scenario). Thats means with the ability at lvl 5 with 30 AP gained from your Rising Tide (20 mins x 60 seconds / 40 seconds = 30 AP) you're healing for 3.75 (natural ability) + 6 (30 AP x .20) x 15 (spell duration) = | 146.25 HP healed over the full duration of the spell |
Now again, I just pulled up numbers from my head and adjusted them slightly after reviewing some items. This also doesn't take into account +AP items. I only played the game this past weekend, so I don't have great knowledge about the game. Obviously the big drawback of the skill would be that the whole team (or whoever wants to heal) would be forced to cluster together in one spot, which is never a good idea. Overall though, this doesn't seem overly powerful, and it would be a new type of mechanic we haven't seen before in a spell.