I AM NOT SAYING THIS HERO IS BAD, SHE HAS A NICHE OF BEING GOOD VS SUMMON HEROES AND ILLUSION HEROES. FROSTBITE IS ALSO A VERY GOOD SPELL FOR LOCKING DOWN HIGH MOBILITY HEROES. I AM LOOKING AT THIS HERO FROM A FUN PERSPECTIVE.
Despite having a high winrate I think Crystal Maiden isn't fun to play anymore. I am very suprised Crystal Maiden still has a high pickrate in pubs. She gets picked sometimes in pro games and she has a high winrate in pubs (her winrate decreases when player rank increases). but I really don't like the state the hero is in. She has terrible base stats and medicore stat gain, no mana, really high mana costs and low movespeed.
I see issues when I look at her spells. For Crystal Nova this spell is far too strong at level 1, meaing her mana costs have to be high in addition to extremely low base intelligence to the point where she can only cast it twice in lane. Then at level 2 if you choose to take frostbite, which you should because arcane aura level 1 is trash your hero suddenly deal 280 magical damage in addition to 6 seconds of CC. Her kill potential with any decent core is very high. While CM should have high kill potential in lane I would prefer having a larger mana pool and more modest mana costs in exchange for less damage at level 2.
Arcane Aura is the spell that makes this hero good. This is the reason why she has always had a high winrate in pubs, especially in lower brackets where people have poor mana mangement skills. In my opinion this is the spell which forces CM to have awful base stats and high mana costs. Arcane aura used to be effective at restoring your mana, but she has been chain nerfed to the point where this is no longer the case. You cast all your spells once and your out of mana. I will give a controversial opinion; arcane aura shouldn't be a global aura. I think the concept of global auras is broken, its too hard to balance. Arcane aura should give allies in a 1200 radius mana regen and spell amp. With a *2 mutliplier for Crystal maiden.
Freezing Field is alot better then it used to be, but why does its mana cost scale 200/400/600? This spell isnt strong enough late game to justify the mana cost. Mana cost should be reduced at levels 2 and 3. Its also a channel spell which doesn't disable your target, making it really easy to cancel at all stages of the game. You have no means to farm a bkb + linkens + blink dagger so you can position properly to ultimate without getting your spell cancelled. Even if you get these items one skull basher proc and your high cooldown ultimate is cancelled. I think freezing field should be changed so it works simillar to sand king sandstorm and monkey kings wukongs command. You no longer have to channel but you must remain in the aoe for the spell to continue. This would make her ultimate alot stronger, its numbers would need adjusting but it would actually be a good teamfight ultimate now, instead of being a spell only useable for ganking lone heroes.