This is a little idea I've been playing around with in the PCgamer demo. Unfortunatly, it won't work in the multiplayer because of creature differences.
Fairly simple idea, just going straight to L2 and instead of land creature chamber build an aquatic one. Archerfish lend themselves to this nicely even if you use a porc head or something since they swim at low level. Thier great range with sight to match and great damage open up lots of opportunities.
First thing I tried was archer-skunks, they're about as weak as it gets but they pack the needed punch and can cloud for themselves preventing massed ranged from winning. Bear fish also seemed good if it gets messy since they are tough with ok meele and good ranged making them good for stalling if they counterattack your base. Though not available in the demo, I'd imagine some lobster-based meele would be a nice compliment for the artillery and could be done cheaply and at low level if you don't use the torso.
Obviously, one of the keys to this is to prevent them from getting some meele amphibians so said meele guys would probably be needed from the start but lobster claws should allow them to kill henchmen fast if they try to mass build the water chamber. I suppose some direct ranged combos such as a porc or frog could allow you to deal with the meeles much better and they wouldn't be worthless for harassing henchmen either.
On the 1v1 map in the demo they can reach the starting coal field basicly forcing them to build a whole bunch of skunk units and play cloud wars or take an expansion. Though I'm not sure if it's all of them, I know you can reach most of the expansion coalfields from the water as well only making things worse for them.
Some brambles at key places might work nicely too... if you can lock them in (or out of expansions) then you'd be doing awesome. Even if the henchmen can swim around the brambles the creatures can't and you could kill them with some meeles. One of their best options is probably to counterattack and stall your O but you can certainly counter their ranged making meele the biggest problem. You have a nice advantage of being able to sit in the water and shoot if their target is close so if you harvest at an expansion close to the water, build your basic buildings near the water, and build amphib ranged then you should be able to counter that just fine as he won't be able to kill your lab before you can get enough porc combos to burst and range attack them.
This doesn't really offer any wonderful endgame possibilities but it seems as if it could slow them down real well and cost them time and cost them seriously in the wallet due to decreasing income and increasing specialized defense costs. As always, if you can screw up thier everything and force them into a specific easy to counter build then that's alwasy a great start so the finishing touches shouldn't be a big deal especially with a decent economy and expansion you have to fend off the counter.