So it's hot and I've decorated my cake and tried to keep it in fridge but when it's out it starts to slip around on the board.  (Using wilton foil.)  It's a giant cupcake cake.  I put frosting under cake to help it stick like I usually do but now its not sticking but sliding.  Do I need to lift it somehow and scrape the frosting off that I was trying to use to make it stick?  Don't really want to stick a dowel through because it's a smash cake.  Any suggestions/ideas?  Thanks

Try thickening a little of your buttercream with icing sugar and adding under the cake as glue. 

Your frosting must be very very thin as I never had that problem.  And living in tropical climate I know what heat is!

Not sure what to do. Could you try and slightly lift it to scrap some of the frosting off???

one word... GANACHE, it will set firm if you use 3 parts dark chocolate to 1 part cream.