Scooby-Doo! And The Loch Ness Monster
The water-going version was a disguised submarine attached to the bottom of Penbrooke's research boat. She could get into it from a hatch in her boat and pilot it around the Loch.
First land-going version
There was additional evidence of the reality of the Loch Ness Monster: the damage it did around the Blake Castle and the footprints it left. (That damage was done by a land-going robot operated by the Haggart bros., hired by Prof. Fiona Penbrooke).
Second land-going version
All of this was done to convince Sir Ian Locksley that Nessie was real so he would take her photos seriously. (The brothers did it more as a prank than for the money.)
- The land-walking version appeared at the end to be made of logs and canvas, but this is impossible. It must have been a robot to have the mobility and destructive power it demonstrated.