I was watching YouTube videos on 3 Combination today.
There are lot of them. Many of them want to 'fix' problems with combination.
IMO, those problems come from not executing 3 Combination correctly.
For example, the second strike is not a back fist. It's a back two knuckle punch. The person in the video made a good point about hurting the bones in the back of your hand if you missed the target with a back fist. The replacement strike he offered in the place of the back fist was a hammer strike, which is the same as the back fist in gross motor skills. I still prefer the back two knuckle punch, which is a linear strike, as opposed the circular strike of the back fist or hammer.
There are also a lot of good videos that show some interesting variations of 3 combination. I'll post links to those later.