This is a potent mix. They also serve the same purpose, namely, regenerating collagen. So why mix them up?

First, all that subcision does is cut the scar fiber that binds to the dermis. In the process, a new scar is generated and you hope that the newly generated scar will fill in the pit. This is especially good if you have deep rolling or boxcar scars. But note that dermal fillers are usually required since there's a good chance that scars will reattach again. Fillers will act as a spacer between the two while you're healing. Unfortunately, not that many success story can be heard from this camp thus far.

CO2 laser, the baddest of all lasers, works from the top. Basically, it incinerates the top layer of your skin. It's like getting a bad sunburn, only 20 times worse. When the new layer is born, you hope the skin texture will appear more smoother than before--so goes the theory. They don't call it "scar resurfacing" for nothing. The verdict is already out though. Even worse than subcision (no surprise there), there's no big improvement of scar pits from CO2 treatment, but only a load of complaints that it will leave you with super thin skin and, at times, orange-peel texture.

So unless your scars are very deep, you might want to reconsider--at least do each separately on different occasion.If your scars are mild to medium, and they're mainly boxcars, go for energy microneedling like Infini. If icepick, go for TCA cross. If rolling scar, then subcision + filler coupled with TCA peel.

Lastly, go through some of the Youtube videos by Dr Davin Lim, the kingpin of acne scars. You'll learn a lot about acne scars. Quite inspiring as well.

CO2 laser can be a double edge sword. There are many types, and a mj is not a mj, namely, lasers state a particular power level but is not 'controlled'. Additionally PD or pulse duration plays a very important role. CO2 lasers are useful in a select type of acne scarring. Some lasers like the Ultrapulse in the Scar Fx mode can get to fibrotic scars, well beyond the reach of microneedling. It is less than ideal as @Sirius Leementioned, it works from the top down. This mean lots of collateral damage before energy is reached to the deep dermal layer. So- some lasers with short PD and high watts can reduce, not eliminate collateral energy loss. Other lasers can get down to a deep level by 'cheating', but not ideal. This is called pulse stacking, and this results in long lasting dots in fractional mode and redness. Additionally the PD can be increased, which gives the same problem as pulse stacking. The 30 watt YOULASER is an example of a CO2 laser that can do this. In burns patients, not really a concern, but for acne scars, this prolonged unwanted side effects can be. CO2 laser in the whole scheme of acne scarring plays a narrow role- best in fully ablative mode in type 1-2 skin shallow box car scars, or pits, or in fractional mode for deep pebble fibrotic scars. Subcision apart from breaking tethered bonds, can also improve fibrosis by remodelling (much like microneedling, but horizontally). Lasers are over rated, I do not dismiss them, they have a role, much like subcision, TCA CROSS, energy based microneedling, fillers, fat transfer, and surgery, it all depends on your scar type. Target the scar type with a method and you have the answer.

My experience seems to be that lasers are better at addressing surface level texture issues like open pores, fine lines, and hyperpigmantation, but not terribly well suited for deeper acne scarring. For that you would want subcision, filler, or some type of RF microneedling device.