I always mix 3 at a time. I put in the eggs, water, oil and sour cream. Mix this well on low speed just to break the eggs. Then I add the cake mixes (one at a time) to which I have added one box of instant pudding to each bag while the mixer is running on low. Once all bags of mix has been added, I turn the mixer up to medium and time it for 2 minutes. Never a mess just well mixed cake batter.