A very flexible and useful build

I've farmed on elite maps and tombs for many times
here is an idea for build

Total 5 active skills and 1 passive skill
pick 4 active skills before going into a map

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learn all 4 of these (15 points)
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Fireball+1/2/3 upgrades (can hit up to 10 targets, I guess)
Frost Bolt+1/2/3 upgrades (becomes AOE only after charging, the 1st upgrade gives it 20% chance to have dmg)
Lifegiver+2nd upgrade (useful to help the team survive)
Knowledge(5)

=--=--=--=--=--=--=--=
pick 2 of these (5 points)
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Gale Force+1/3 upgrades (gale is AOE even without charging, can only hit up to 4 targets)
Time Shift+4th upgrades (root effect only happens after charging)
Arcane Shield+1st upgrade (15sec duration + 30sec CD = 15sec without Shield if you don't charge)

=--=--=--=--=--=--=--=
if there's 1 rest skill point, Maybe spend it on:
Fireball 4th upgrade,
Time Shift 3rd upgrade,
or one of Arcane Shield upgrades

choose Arcane Shield only if you want to prevent getting 1-hit kill from boss at Elite Rook's Nest
which a best set of defensive gear will do
or whatever the reason is

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btw
Lightning is pretty useless, AOE is the only thing matters

Why?
You don't need it at normal map, cuz the monsters are too weak anyway.
In the elite map, monsters are too strong for Lightning to make a significant inpact especially for a group of monsters.
For boss fight, Lightning has less DPS than Frost, and
compared to Gale, the small boosted DPS Lightning made doesn't really help.
At last, Lightning cannot help you to have greater DPS than Rogue on Single Target.