============== GLACIAL CASCADE MECHANICS EXPLAINED ==============
1. GC is not a projectile, so any sources of increased projectiles like Dying Sun or Greater Multiple Projectiles will not work. The only thing you can manipulate is it's AoE on Initial and Final Burst.
2. Final Burst has 100% more AoE and deals 200% more damage. You can actually overlap one of the Initial Burst with Final Burst, however it's very difficult and it requires you to always cast Glacial Cascade from optimal distance
which is not always possible. If you want to deal optimal damage, try to hit a boss with a Final Burst which should be around your edge of a screen.
3. This skill can knockback enemies, which makes fighting any melee-based mosters much easier.
4. Try to get a feeling with your Final Burst AoE with 4 Intensify Stacks to deal maximum damage to bosses.
============== LEVELING GEAR ==============
There are tons of uniques that can carry you through the campaign, I'll list anything that either I've been using or what is reccomended
Number in brackets are level required to wear a unique
1-H Weapon: Axiom Perpetuum(10) -> Void Battery(68)
Off-hand: Axiom Perpetuum(10) -> Kaltenhalt(16)
Helmet: Goldrim(1)
Body Armour: Tabula Rasa(1) -> Tabula Rasa with +2 to socketed AoE gems (20) -> Carcass Jack(62)
Getting a 5-link Carcass Jack should be enough to carry you until red maps
Gloves: Lochtonial Caress(1) -> Asenath's Gentle Touch(25)
Boots: Wanderlust(1) or if you're rich Seven-League Step(1) -> Replica Inya's Epiphany(61) - Don't equip them until you have Disciple of the Forbidden allocated on the tree
Amulet: Replica Karui Ward(5) -> Astramentis(20) - Don't pay too much attention to a roll on it, you can always use 20 Intrinsic Catalyst to gain extra attributes
Rings: Berek's Pass(20) and Berek's Grip(20) -> 2x The Taming(30) - If your resistances are fine, you don't need to swap since Berek rings give more damage during a campaign
Belt: Meginord's Girdle(8) -> Belt of the Deceiver(20) -> Replica Prismweave(25) - I honestly didn't use Replica Prismweave, but it should give you a decent damage
For flasks, just use Life and Mana flasks, Jade, Granite and Quicksilver, swap out mana flask for Taste of Hate(20) once you no longer have mana issues
If you don't use a unique in some slots, just get generic Life, Resistances and probably look for ES or Armour/ES bases
============== LEVELING GEMS ==============
HUGE DISCLAIMER
I honestly do not reccomend league-starting with this build. This is basically my take on comfortable mapping once you're a few weeks into a league an you just want to chill-out casting big icy spikes.
The entry cost is very low and you can get to early red maps in less than 2 divines(400c) budget.
Here's how you can level a character for first 5 acts of a campaign until you'll get access to all gems.
You cannot use Glacial Cascade until Level 28, so we'll be using variety of cold skills until then
==============
Start with creating a Scion character, kill Hillock and drop everything from this character to the stash - Congratulations, you've successfully created a MULE character to get Onslaught support for Witch
Then choose a Witch and use it as a main character
For the majority of your leveling most of your links will be blue except Hatred(24), Added Cold Damage(8), Onslaught(muled from Scion) and Vitality(10), this changes after Act 5, however it's a bit easier to recolor your gear at this stage
Level 1 get Freezing Pulse, link it with Arcane Surge and use it to get to Submerged Passage and kill Hailrake for Quicksilver Flask
Level 4 pick up Frost Bomb, Frostblink, try to link Onslaught to any skill and also try to link Summon Phantasm to either Frost Bomb or Freezing Pulse
Level 8 pick-up Added Cold Damage and link-it to Freezing Pulse(swap-out Onslaught if needed)
Level 10 you can get Vitality and Clarity auras as well as Flame Dash which you'll spam until getting Shield Charge in Act 6
Level 12 pick-up Creeping Frost and you can link it with Efficacy and Lesser Multiple Projectiles. You can use this set-up as a main clear instead of a Freezing Pulse
Level 16 pick-up Herald of Ice and Herald of Thunder. Be aware that you might not be able to reserve all of the auras, so drop Herald of Ice first
Level 18, you can pick-up lots of support gems, Controlled Destruction and Faster Casting. Link Controlled Destruction to a main skill and Faster Casting to a Flame Dash or any other secondary skill
From this point on you can also pick-up lots of other cold skills like Wintertide Brand and Cold Snap, however it's lots of buttons and can be overwhelming to play if you're not experienced in campaign runs
Level 24, get Frostbite and Hatred. Start using Hatred ASAP by dropping Heralds, or at least level it in your off-hand
Level 28 finally we can use Glacial Cascade
For gem links past level 28, go to Skills Tab and look on the order of supports for a reference in leveling section
Try to look at it mostly once you've finished Act 5 and cleared Twilight Strand in Act 6.
============== As some extra side-notes for leveling ==============
You'll have mana problems and that's hard to avoid until you'll have leveled-up Clarity paired with Inspiration on your main skill
Don't mindlessly level-up Vitality and Clarity to a max level. You need some left-over mana to play the game. It's sometimes better to wait for mana from leveling up.
Don't feel discouraged if you can't equip all the gems. If you have a main skill with auras and mobility, that is enough to get you through the campaign
Use Molten Sheill on left-click to have your defences uptime as high as possible.