This could be useful.
What I do on my server is I have a default minigame, and at the spawn room there's a choice of different playertypes: shark, dog, fish, tank, etc
And a choice of different sizes: large, normal, mdsmall, small, tiny
As well as a silver brick that's used to take you outside if you get too big/if you're a fish it drops you to water, but despite the fact that it CONSTANTLY tells you to use the silver brick while you're in the spawn room, very few people use it. /rant