I love the idea of the monkey engineer and his cleansing foam, but it's really annoying how he shoots it randomly. If you place him where he covers a lot of track, the foam doesn't always cover the entrance, and if you're really unlucky, bloons can get through without touching the foam at all. But if you place him where his range barely touches the track, you're pretty much wasting his turret potential.
There should be an achievement for getting them all.
and just a tip: in my opinion, the best character is birdman tribe leader. Flying is really useful for just skipping levels you already have all the characters in and navigating though annoying jumps to get to certain areas. Also, the staff attack is ridiculously powerful.
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