This sounds like a party your daughter will never, ever forget!!!
And that's what life is all about is making special memories!!!
How creative you are!!!
Enjoy the party and do let us know how it went!!!
As for a "messy cake", you could "decorate" it with crushed Oreo's to make it look like you got it out of the trash!! Or have cupcakes or brownies and let them decorate with Oreo dirt and gummy worms, etc...
Do you have a "dress theme".....like telling them to come to the party in their dirtiest, ugliest clothes!!
Egg toss is always fun and messy!! Feeding chocolate pudding to each other with each being blindfolded!! It's a team race to see which two finish all their pudding first!! Chocolate is definitely the messiest!!!!
Have lots of fun and Happy Birthday to your daughter!!!!
hugs,train