So I'm DMing my first campaign and have a plan for the final battle between the PC's and this massive Bio-Mech created by the ancient gods, but I want to know if anyone knows IF this idea is even possible, and if so, how to pull it off. Basically, at this point in the campaign, the PC's would have encountered a monster/construct 1,500 feet tall that they think is being controlled from the inside by the main villain. With the help of many NPCs at this point, the party would find and refurbish their OWN ancient mech that should be comparable in strength. If they go the route I expect them to (they usually do) some of the party should be controlling this mech while the rest climb aboard the Villain's and try to take it out from the inside.
Now here are the specifics that I'm not sure are possible. There would be two encounters going on at the same time: The two mechs fighting outside that cause the party inside to roll DEX saves to stay on their feet, and the party inside basically going through what amounts to a dungeon to disable some of the enemy mech's systems (giving their mech a better chance to win) and reach the villain at the top. How should piloting the ancient mech work? And is the rest of this idea even possible?