How to make fluffier frosting without an electric mixer?!

Homemade buttercream frost? Maybe it needs to sit and thicken/cool before you can start mixing and getting it fluffy? If you mixing with a spoon, try mixing with a wire whisk. Add a tiny little bit of cream of tart? Add more 10x sugar or cream cheese or whatever the main ingredient is. It might thicken it up and get it to be less water-y/syrup-y.

Are you using the old "wooden spoon" , a fork or a whisk?

If you are using spoon or fork it will take forever, I use a whisk when the mixer quits. put the handle of the whisk between palms and rub back and forth as fast as you can.

Add almost enough powder to make it spreadable, fold in a ccarton of whipped topping.

I have cream cheese frosting in a ziplock bag that will get whipped topping in it next week when I start getting ready for a work day here at the ranch.

My recommendation is to go purchase an electric hand mixer. They are not that expensive.

I don't think you made it right. Buttercream should NEVER be syrupy. I don't know how you made it, or what you put into it, but usually buttercream is powdered sugar, butter, vanilla and a little milk or cream, after you beat it together it should just be fluffy. If it's syrupy it may be that you put too much liquid in it.

This may sound weird but, Say its chocolate frosting, add about 1 tablespoon of chocolate instant pudding mix. Vanilla frosting would be vanilla pudding mix. Good luck.

Put it in the freezer and let it thoroughly cool if you have time. Then add 1 tsp. cream of tartar and whip it with a whisk if you have it.

Use a tiny bit of baking powder and whisk in some lightly beaten egg whites.

Should make your icing nicer and liger. Add flavour - add colouring too if you so desire.