A very effective Jaina build.

Adaptation Choices:
Tier 2: Arcane Intellect or Envenom
- This build will likely be doing a lot of damage and I truly don't find Envenom to be that necessary even though it is good. Arcane Intellect has great synergy with the build and allows some versatility. If you have a squishy you think will be giving you a lot of problems, then Envenom may be the choice.

Tier 3: Frost Armor or Ice Floes
- Yes, Ice Floes. It's really good here. I would only take Frost Armor if the enemy comp really calls for it.

Tier 5: Sprint or Icy Veins or Improved Ice Block
- Sprint is basically a must on Jaina, but I find her true best defense is offense. Icy Veins with Arcane Intellect and Ice Barrier lets you put out tons of damage non-stop with a shield return if there are multiple targets. Improved Ice Block should only be taken rarely when you might have to deal with annoying Heroics.

Tier 6: Ice Barrier or Northern Exposure or Numbing Blast
- Ice Barrier with the mana return from Arcane Intellect and Icy Veins will keep you shielded surprisingly well if there are multiple targets. If you take this, try to engage when you will be hitting enemy minions with your AoE as well. It gets ridiculous. Northern Exposure is really good with Ice Floes for team fights. Numbing Blast is also good if your team needs the extra lock down.

Tier 7: Bolt or Wintermute
- Bolt is obviously one of the best choices most heroes like Jaina can take at 20. However, because of the build synergy, Wintermute can add SOOOOO much more damage and just delete everything. It's unlikely you'll really need the extra damage, but if you do, take Wintermute for the overkill. I find it's really more of a win-more pick.