I start by washing the watermelon well and patting it dry, then slicing a flat base off the bottom so it won't roll around on the table. I lay it on its side and use a marker to sketch a rough skull face across the middle third, including two large oval eyes and a jagged, triangle-toothed mouth.
Using my chef's knife, I slice off the top third of the watermelon above the sketched face, keeping the cut as level as possible. I save this piece because it gives me extra fruit to scoop and use later in the bowl, so nothing goes to waste.
With a large spoon, I scoop out all the pink flesh from inside the watermelon, leaving about half an inch of red flesh against the rind for sturdiness. I cube up whatever flesh is still usable and toss it straight into my fruit mixing bowl.
Following my marker lines, I carefully cut through the rind to create the eye sockets, nose hole, and zig-zag mouth, removing the cut-out pieces of rind as I go. I take this part slowly since clean lines make the skull look far more convincing once it's filled.
I wipe the inside of the shell dry with paper towels so the melted ice or condensation doesn't water down my fruit later. If the watermelon wobbles at all, I trim a touch more off the base until it sits flat.
In my large bowl, I combine the grapes, blueberries, cantaloupe, honeydew, strawberries, pineapple, blackberries, and reserved watermelon cubes, then squeeze fresh lime juice over everything and toss gently so every piece gets coated.
I spoon the fruit mixture into the hollowed-out watermelon skull, piling it slightly above the rim so it looks generous and full. I tuck kiwi rounds near the eye sockets and scatter a few mint leaves on top for a pop of green.
I pop the finished bowl in the fridge for at least 20 minutes before the party starts so the fruit is cold and crisp when guests dig in. Serving it chilled keeps the whole display looking fresh for hours.