Arctic Armor almost imba.

There is no logic in Arctic Armor not working with Reduced Mana gem and/or Blood Magic.

Reduced mana applies coefficient lower than 1, therefore, lowering total costs of skill--you can argue this is only for the initial cost of skill but than you run into auras where it works with the reserved amount, which is clearly not the initial cost of the skill.

Now Bloodmagic is more controversial but again, the support gem description says the following:
"Spend Life instead of Mana for Supported Skills". Bloodmagic keystone is even more specific because it states in addition to the above that it "Removes all mana".

The game currently do not have "channeling" costs for skill but there are degen effects already implemented so the mechanic can not be completely out of the picture.

All in all, if it is supposed to be working with INT/mana users, the intention and design is very poor. % based auras are good example because they can be used with Bloodmagic but the drawback is just too big for anyone using Bloodmagic to cope with it. Arctic Armor is a skill that excludes Bloodmagic users completely and without remedy--no consideration of drawback vs benefit, the skill is just not usable.

I also wonder who is the targeted mana user because rangers can be right away removed from the options due to extremely low mana pool and extensive usage of auras. INT based spellcasters are an option but the selection is rather limited if you consider that there will be summoners and totem users that have literally no use for this skill. There are STR and STR/DEX based characters that will be struggling with mana most of the time, hence most charactes from this group pick Bloodmagic. What is left are end-game characters who often spec out of Bloodmagic, replace it by Bloodmagic support gem and load themselves with auras fuelled from mana pool. So who should be the user of this new skill?