This build offers good damage in 2 different elements to reduce reliance on an infinity merc on hell difficulty.

Skills:

Firetab:
warmth - 1pt

Lite tab:
static - 1pt
tele - 1pt
lightning - 20pts
chain - 20pts
mastery - 20pts
prereqs - 1pt

Cold tab:
icebolt - dump after everything else
frozen armor - 1pt
orb - 20
mastery - 1pt
prereqs - 1pt

Stats:
Str - Enough for gear
Dex - None
Vit - Everything else
Nrg - NONE

Gear:
Occy - socketed with ist
Spirit monarch - highest fcr you can get
Shako - socketed with ist or ptopaz
Tal armor - socketed with ist or ptopaz
Tal belt - 15mf is pretty cheap so shoot for that
Magefist or Chancies - fcr or mf
Wartravs - Highest mf you can get
Tal ammy - 2 skills and 3piece set bonus ^.^
Nagel - 30mf if you can't get, just get the highest you can
SoJ - this is a must for the boost to our mana pool! (you can do 2 if you'd like, but only 1 is needed)

Charms:
Sorc Torch - Highest you can get
Anni - Highest you can get
Gheeds - Highest you can get

Merc:
Act 2 nm Defensive ofc! ^.^
Gladbane - Eth if you can get it - socketed with shael
Gaze - 20DR and eth if you can get it. the DR is more important though.
Reapers Toll - Eth if you can get it - socketed with Shael

Stats:
10k lite
4.5k chain
640 orb
105 fcr (8th frame)
You should pull close to 450mf and 508 if you use ists and get perf mf on your gear.

Mfing with this build is pretty simple and easy. Use chain for groups, lite for bosses and orb for lite immunes.
Your merc can handle any dual cold/lite immunes that may spawn.