The playset depicted a battle between the King of the Monsters and a three headed aquatic monstrosity named the Tricephalon Monster. Kids (or adults) could enact a massive battle between the two titans in the middle of a major city. The playset included :
the Trcephalon Monster
3 Civilian Vehicles
2 Jet Fighters
1 Police Car
Shell Firing Battle Ship
22" x 28" Diorama
30' x 30" vinyl play sheet
I remember finding this in the aisles at Toys R Us back when I was a kid, I was so excited I nearly dropped a brick. Of course my parents got the playset for me and I wore that thing out playing with it. I had the Godzilla and Tricephalon for years after the rest of the playset went the way of all things, Unfortunately the pair were lost during my move from my parents house to my first apartment but I still have the memories.
And I will reclaim those figures again.....oh yes I will.
Just as an aside, HG Toys made a series of Godzilla puzzles with some killer artwork like the playset box.