When you start in the game you have no good items no money and not dying all the time can be a challenge in veteran difficulty. This build fixes most of those problems.

Why it's more fun than most builds out there ?
Prismatic bolt is very powerful and easy to play, but do you really want to play 50hrs or more of only right-clicking ? It will bore you to death and you will not enjoy the game very much. Shooting 30 silly little missiles will never give you the "I'm the king of the world muahahaha" feeling that frost wave provides.
Fire magic has one problem it's slow, blazing pillars move around slowly and not always where you want, infernal collapse and firestorm take a while to cast and do their job too, hailstorm and ice prison are almost instantaneous and frost wave at (10) becomes really fast.
Ice skills have less/no cooldown allowing you to benefit from cast speed bonuses, frost wave spammed with +70% cast speed is something else than seeing fire pillars crawl around trust me ;)

Upsides :
- free hp/mp regen, less money wasted on potions after 33 and none after 53
- damage is 100% player level-based, does not require good items to work
- good attack/defensive skills
- empty your screen of enemies in 1-3 skills
- great damage on single target (1mio+ at lvl100 with the right gear)
- fastest class to farm items at high lvl scratch that berzerker class with rampage+savage rush+haste spell goes insanely fast, it's still very good ;)
Downsides :
- you need to be at very close range to do massive damage making it unsafe for elite hardcore :(

This build is recommended and guaranteed to put a smile on your face in :
- all softcore difficulties
- casual,normal,veteran hardcore (not elite hc sorry or rather it works but you will definitely need to grind for items)

Inferno
Charge Mastery 3 lowered it because it's unecessary
Fire brand 2
Frost
Hailstorm 15
Frost Phase 15
Elemental Boon 15
Frost Wave 15
Ice Prison 15
Frozen Fate 15
Ice Brand 15
Storm
Prismatic Bolt 1
Death's Bounty 15
Lightning Brand 2
Prismatic Rift 15 it almost never triggers even at 15/15 it's really not that good

main attack combos :
elemental boon->death bounty->hailstorm->frostwave
death bounty->frost phase
ice prison->ice prison

Active skills and why they are good :
elemental boon - ice damage buff + elemental defense
death bounty - free hp/mp regen for you and your closest ally, 100% stun at 15/15 giving you time to kill them before they even make one attack
hailstorm - ice debuff and slows/stuns ennemies also does very good damage
frostwave - damages almost everything on screen when you unlock 3-5 waves and does ton of damage at point blank because all waves hit the same ennemy, it works like a shotgun the further away from you the less damage so don't fire it from the other side of the screen, wave also fills your charge bar very fast
frost phase - at 15 the knock is enough to kick a champion half a screen away, great "get away from me" skill if you teleport on yourself, enough damage to 1-shot small ennemies if you're lvl100, fast move around skill
ice prison - with 1 point you can already cast it around you for defense, block a corridor with it preventing ennemies to come at close range, block a champion/boss and at 15/15 it still has all those great functions but with infernal collapse damage...except it's instantaneous to cast, you cast it around a champion, re-cast it 2s later and either he's 1shot by the explosion or will loose a good chunk of health 100-200k damage easily

Recommended passive skills :
Ice brand - if the ennemies survive your 1st hailstorm they pretty quickly won't a 2nd because of the ice brand damage
Charge mastery (10) - not an obligation but it will help a new player without mana regen socketables, more than 10 is useless
prismatic rift - not really necessary but it will also help you survive by teleporting/interrupting ennemies that hit you giving you time to destroy them before they do it again
frozen fate - while playing elite hardcore as mage I realized this was very useful at the beginning, it will randomly freeze enemies around one you just killed and can sometimes give you time to safely spam attacks on a paralyzed champion

Stats points :
1) raise VIT up to 25 to be able to equip better armor parts at low level and have a slight shield block bonus
2) max FOC until you reach 364 (lvl105 unique armor set requirement)
3) after that it's how you want, it's probably a good idea to keep maxing focus

Skills progression :
2016 edit : you can enjoy a very playable prismatic bolt while still playing this build
changes I made since the original version :
3 charge mastery max (i played elite hc without shared items with that it's enough)
5 prismatic bolt
2 fire and electric brands
max frozen fate
oh and...if you have unspent skill points don't waste them keep them until you can upgrade the right skills

- level 2 : prism bolt (1 only until your are in act3)
- level 3 : charge mastery
- estheria : unlearn magma spear
- level 4-6 charge mastery (max 3!) > frozen fate
- level 7 : hailstorm
- level 8-13 : hailstorm > frozen fate
- level 14 : frost phase (1) > ice brand > hailstorm > frozen fate
- level 15-20 : hailstorm > ice brand > elec brand (max 2) > fire brand (max 2)
- level 21 : elemental boon > hailstorm > ice brand > frozen fate
- level 22-27 : elemental boon > hailstorm > ice brand > frozen fate
- level 28 : frost wave > death bounty > elemental boon > hailstorm > ice brand > frozen fate
- level 29-32 : frost wave & death bounty (max you can) > elemental boon > hailstorm > ice brand > frozen fate
- level 33 : frost wave & death bounty (max you can) > elemental boon > hailstorm > ice brand > frozen fate
- level 35 : ice prison (1) > frost wave & death bounty (max you can) > elemental boon > hailstorm > ice brand > frozen fate
- level 36-100 : frost wave > death bounty > hailstorm > elemental boon > ice brand > primsatic bolt (max 5) > ice prison > frozen fate > frost phase

Wand+shield
no good reasons to play with a staff in TL2 especially with this build
if you play in casual-normal or softcore veteran you could equip two wands giving you more bonuses instead
if you play softcore/hardcore veteran-elite you will never survive without a shield, even if you somewhow manage to beat the story with a staff without dying once, after lvl 50 even in veteran you will start to get 1-shot all the time, mages have 0% all damage reduction from the start, engineer and berzerker take 25% less damage
And think that the "endgame" in TL2, where you will get the easiest and best loot is surviving NG+ tarroch tomb lv200 bosses.

Weapon socketables
+% cast speed (+3 +4 +5 +6 chaos ember you can get by transmuting elemental embers you don't use)
+% crit damage (chaos gems too or a few eyes/skulls like eziro,manticore,rambren)
+% crit chance (bondron,whorlab skulls)

Gearing yourself easily
- Go to act2 asap, you have until level 25 to gamble probably the best items for this build.
Why 25 ? because after that the gambler NPC will sell you worst items, yes in this game low level items can be very powerful.
- Reach act2 around 20-23 and then immediately go to the green sidequest and complete it to unlock Duros the blade, once you free him from his prison go back to town and check for those prices, if you don't see them and you are close to level 26 quit-reroll the world until you get them.
Prices are not a 100% chance but a good 70-80% to get the right items.
- Glorious 1h sword +15%cast speed +15% charge 2970 3190 (buy 2 of them if possible)
- Suicide wand +20% all damage (highest % in the game you can buy 2 also if you want +40% on prismatic bolt) 3410 3520 3630 (gold of course)
- Roundheaven shield 29% block chance (only block chance is useful in tl2 and you won't find more until lvl 98..no this is not a joke it's now or never to avoid almost 1/3 of attacks)
- In act3 once you unlock sundered battlefield go check the left of the map, there will be a mining area with dwarves, explore it and try to find a "notch mine" it's a minecraft easter egg, there you can get a useless for attack but very good for defense "wooden sword" it gives +18% block chance (remember my build does not rely on weapon damage so it's totally ok to use it, I sure did in veteran when I was killing +20 level mobs in mapworks lol)
if you don't see notch mine you can quit reroll and frost phase-death bounty your way there..while you're at it try to get 2x iron swords and place them in your 2nd weapon slots, switch send your pet switch back and poof 1s pet to town travel !
- once you unlock mapworks check the gambling robot for this shield : 5115 5362 gold the centerwing, it has a good 21% block chance and +15% cast speed (I use it with all my heroes in veteran and elite tarroch tomb)
- the best set for us is sentinel so check as often as you can in act4 minehead or mapworks for parts of it with good bonuses (I keep parts with 500-700hp or +14% cast speed the rest i transmute together with highridge to eventually get a better sentinel part)

SORRY NEED TO MAKE A NEW VIDEO
Video shows the build with gear collected and enchanted to beat tarroch tomb in NG+

this is the set I use, built mainly for my wolfpack berzerker (who badly needs mana steal) but it works as well for a mage or for any other class and build really.
http://torchlight.wikia.com/wiki/Sentinel_(Rare_Armor_Set_-_TL2)

If you have a compete Emberweave armor set use it instead, it allows to socket +1540hp skulls instead and has the same +33% cast speed
http://torchlight.wikia.com/wiki/Emberweave_(Unique_Armor_Set_-_TL2)

- Sentinel set parts with only +health bonuses :
as long as you stay in the 1st playthrough minhead vendors will always sell various sentinel parts
you can quit the game and reroll the game to check if there are good parts, rince & repeat, you can also do this in act3/4 to get an exorcist,dwarfking set too
- limoany skulls :
limoany you can only drop in lvl 55-65 maps in mapworks BUT under player level 62 after that the "area" will be too high level to give you limoanys so you will have to "sacrifice" a character to new game plus, in new game plus act1 frosted hills the "area" is always of the proper level so you can find them in chests whatever your level is
- Meerko skulls :
often drop them in ng+ act2 ossean wastes while chasing the golems to open tarroch tomb
- Weapon :
wand giving me increased cast speed, since legendaries don't drop that easy cough luckily there are alternatives
wooden sword (reroll game check the mine area in sundered battlefield) : +18% shield block, no attack bonus but you really want better block instead if you play veteran-elite
glorious sword (gambled in act2 for 2970 gold) : +15% cast speed +15% charge
snow witch scepter (gambled in act3 for 5500/5720 gold) : +9%cast speed also critical increase
any other wand giving you +% critical damage if you want to do crazy numbers get a netherrealm 4 slots wands and socket rambren skulls in them (+60%crit damage each)
- shield :
roundheaven (gambled in act2 if you are below lvl25 for 2227/2392 gold) 29%block chance, no better shield till a long time, shield block is the only thing that matters not physical armor
the centerwing (gambled for 5362 in mapworks but dont remember which lvl i was) 21%block 15%cast speed...nice

keep in mind this is aimed at console/vanilla players NO MODS NO CHEATS
with infinite gold you can enchant everything and break the game you don't need a guide, unless you want to be even more powerful ;)

PLAYLIST LINK
https://youtube.com/playlist?list=PLVnGcNELvFOVbOsVmxAQee0PNQIVGBTcb

LV 04-21 LEVELING SELF FOUND ITEMS
https://youtu.be/ARZsm-5wqSM

LV 20-21 REGENT BOSS AND GAMBLING NPC UNLOCK
https://youtu.be/8RL78uco_vg

LV 21-24 PHASE FARMING ACT1 CRYSTALS AND GAMBLING UNIQUES
+ BONUS DEMO AT THE POWER YOU HAVE AT LV55 AT THE END
https://youtu.be/iX4HR9pXx_Q

LV 24 HOW TO HUNT THE PHASE PORTAL IN OSSEAN WASTE AND WHY YOU WANT TO PROFIT FROM IT AS MUCH YOU CAN (CAN TAKE HOURS TO FIND THE GOOD ONE)
https://youtu.be/W3_Oo9IK3FE

LV 25-30 PHASE FARMING ACT2 JACKALS, WHAT TO TRANSMUTE AND MANTICORE BOSS
https://youtu.be/ttBfzFsE8bI

LV33-36 FINALLY FROSTWAVE AND A USEFUL DEATH BOUNTY
https://youtu.be/9Op1iegr7e8

LV44 ACT3 MIDDENMINE DYNAMITE QUEST REWARD CHOICE AND SOCKET ENCHANTER
https://youtu.be/otaXDCheRk0

LV45 PHASE FARMING ACT3 SUNDERED BATTLEFIELD LAVA ROOM JOSKIN SKULLS
https://youtu.be/vUheLgdfbP4

LV53-55 LV53-55 NETHERLORD BOSS MAPWORKS HOW TO GET SENTINEL SET AND WHY + ENDGAME GEAR +MAPWORKS + SHIELD BLOCK AND OTHERS
https://youtu.be/gJ9Sqj7CcDU

sorry previews don't work for some reason replaced them by links