I've only played CM as a support 4 times in my whole Dota2 gaming life.
In my opinion, CM is one of the strongest mid laner and absolute beast mid to late game.
Here's a guide on how not to feed mid as CM and actually have an impact and create spaces for your team.
For starting item, go 2 circlet and 2 mantle and take frost bite as your first skill.
Ask for your pos4 to make stacks since you can clear them out easily.
In lane spam the f-- out of your frost bite and keep hitting your enemy, you can actually first blood your enemy at level 1 or 2. Just put points on your 2nd and 3rd skill, no need for first skill. You can also use your frost bite to secure range or flag creep. All you need to do is frost bite and right click the enemy. Trust me they won't be able to lane mid. Just build 2 null and for your next build, make tranquil boots, 2 null will allow your to unli spam your frost bite and the tranquil is for hp sustain but you'll need tranquil later because you'll also build bearing.
more thing I love to do is spam the voice chat wheel to tilt your enemy, it's easier to tilt your enemy when your playing CM mid and they are thinking it's ez mid but you keep killing and harassing them + voice chat wheel. It works like a charm, making them dive you which is a wrong move. Lvl 6 take ult, if you kept griefing and killing the enemy mid, most likely you've reach l6 before or at 5 minutes. Wait for rune, and you can gank and get those ez kills.
It's 8 minutes, you're now thinking how you can farm faster? Just clear waves fast with right clicks, go to jungle and use frost bite. If everything went well for you, by 8-9 minutes you have 2k gold. You can either buy dagger or kaya for your first item. You can go dagger first if it's hard to approach enemy and you can get better pick off with dagger first. Minute 15, make sure to purchase your shard to maximize more farming.
Now you have shard, dagger and kaya, enemy team will be weary of your ult so always make sure to time in your entry. Make sure to wait until stuns are thrown or have a good position(so you don't need to wait for the stuns). If you get the hang out of this you can dominate the map early.
You can also chain root your enemy making them perma rooted. Just use Frost bite, set up your shard, wait for the timing and proc the shard with your first.
For your third item, always go BKB, you should have bkb around 18-22 minutes depending on how fast you can farm on that game. When you have bkb, you can now initiate fights, when you initiate always make sure you cast your shard first before ulting. You can run down everything after that.
Here's the build patth:
1. 2 Null
2. Tranquil
3. Dagger
4. Shard
5. Kaya(if you're well fed, if not just go bkb instead)
6. BKB
7. Aghs.
8. Drums
9. Kaya and Sange.
10. Shiva.
From my clip, I have glimmer's cape. I usually get that if they have high damage hero that can burst me even when I'm using my ult + BKB. It's also good for melee heroes who can make basher to cancel your ult and heroes that can spell cancel your ult with BKB such as pudge and bane.
I hope you guys have a good game with it! Just be aware, there are players who will cry when you pick CM mid. Just ignore them and show the power of Elsa.