In the mobile version at least, MvM is an excellent way to make Bloonstones. The first attack per day earns you 5 stones, and subsequent attacks give you 3. There's also a 2 stone bonus for attacks you send that win (or are ignored by the enemy).
I rarely if ever defend against attacks, and it seems like a good 90%+ of other players ignore them as well. In the mobile version, there's no XP gain for winning, it's just cash, honor, and Bloontonium, which refills automatically. The only reason I care about honor is for achievements.
Cash win/loss wise, I've got so much cash that I don't even pay attention to it. My capacity is around 200k gold, and I have 1.8m. Aside from retrying boss fights, there's nothing to spend it on. I believe in general if I attack as often as my Bloontonium is full, I'll end up profiting.
Honor-wise, staying at low honor will probably end up pitting you against weaker opponents, although I think I generally gain honor by attacking as often as I can and losing every attack. Currently I'm at around 10k honor from this strategy. The losses are so slight compared to the gains that it's hard to stay low.
The difficulty of each piece of land relative to the player's level
and choice of buildings can be inferred from the number of dots,
ranging from one coloured in dot (trivial) to five coloured in dots
(very hard) or five dark colored dots (impoppable). Some tracks on
certain tiles are notably more difficult than others, and thus those
tiles will have a slightly higher difficulty rating than tiles near
it. Most tiles will restrict a player from using one or two towers,
such as water tiles, where one can not use Ninja Monkey towers or Bomb
Shooter towers (Excluding the special mission 'Shipwreck' or 'Sub
Alliance' in Mobile)
Source:
Bloons Monkey City Wiki
It goes into more detail on that page, but it deals with the dots under the balloons and what color they are.
Best Answer
"Water's Edge" terrain means "land on the edge of a body of water." Note that it's a land tile, not a water tile. Rivers and Lakes both count as water tiles, so just pick a land tile right next to one of those.