OPM does indeed confirm Rampo as Tribalstack Tropics' boss.
I agree with some of you that he doesn't quite look like a boss; I imagine more of a 'mini-game baddie', a bit like Mr Vile, or Motzhand (could they be deemed bosses as well?). I guess you have to roll up the ramp and hit his eye, or something, whilst dodging what he spits out, which seems less of a battle and more of a 'game' to me (I'm aware of the meta irony).
Until we see more, we can't say for certain what it will be like, but it does look interesting and fun, and it probably serves the purpose of teaching the Reptile Roll move to newbies. Maybe just not the type of 'boss' people were expecting... though this is just the first world.