Hahaha, cool map! I loved the flag effect.
Here's some idea for future additions:

-What about warping pipes? I think i already have an idea of how you could implement it: area trigger checking if there's a single player and is crouching to trig a teleport to another tube. With a little bit of tweaking you could even implement a fluid animation when the player enters and gets out.

-A tube with a carnivore plant would be cool (maybe randomly activated only in some matches)

-The sun and the clouds in the BG!

-Moving toads or turtles would be amazing, but even simply a kickable shell or a static toad to splat would be cool

It's a real pity there's no custom sound support yet, this map would be an awesome candidate.

Hope you find these ideas useful