The Tribal Turtle and Pat Fusty are the only towers and Special Agents that can be placed on both land and water.
The Tribal Turtle can be placed half on water and half on land.
The first three Daily Challenges after the Tribal Turtle update all provided some free Tribal Turtles. The first two gave one turtle, while the third gave two.
April 7, 2012 had a Daily Challenge that gave 8 free Tribal Turtles.
When the player places a Tribal Turtle on water, there will be ripples around it. When placed on half water, half land, the ripples won't appear.
This agent is the only non-pro agent that can pop Lead Bloons in a normal situation (the Bloonsday Device uses an ability and the Angry Squirrel needs to be enraged). However the Tribal Turtle can't pop leads with both attacks.
When the Tribal Turtle is first placed, it has both the spear and coconut in its hands. The Tribal Turtle will throw both the spear and coconut on its very first attack, similiarly to its pro version.
While its ability to be placed on land or on water may seem interesting at first, it would only be of benefit when you are severely cramped for space and there is a small part-land part-water spot you could place it. (This is assuming a Special Mission where the towers/map never change around). In any other event, just place a left-path sniper if you need a land-based tower that good against ceramics and lead, or put a right path buccaneer or submarine if it needs to be water-based.