Karchev the Terrible... or as I like to call him: Karchev the Awesome!
I love Karchev. Karchev is everything every other 'jack 'caster wants to
be. First off he's ARM 19 with 34 boxes, so he's crazy hard to
assassinate. His spell "Unearthly Rage" gives 'jacks in his
battlegroup and control area boosted melee attack and damage rolls so
even the humble Berserker is hitting DEF 15 on average rolls, and with
Tow he can get a friendly 'jack into an enemy 15" from where he starts
the turn. He makes our slow and inaccurate 'jacks fast and accurate,
covering their biggest weaknesses. He also assassinates like a boss, he
can trample over any small based models in the way (with boosted attacks and damage from
Unearthly Rage) and his axe is POW+STR 19, which is nothing to sneeze at.
He can charge something 11" away (SPD 4, + 2" Arcantic Turbine, +
3" charge, +2" reach) with Pathfinder so sometimes a 'caster who thinks
they're safe from his apparently low SPD 4 can be in for a rude shock.
On
the down side he's only got 5 focus, 3 of which are generally spent casting Unearthly
Rage and 1 upkeeping Tow, so he needs very focus efficient 'jacks with
lots of initial attacks or rules that trigger more free attacks - you
can't afford to be giving them focus you don't have. Berserkers are
excellent (2 initial attacks + a chain attack, and they can charge for
free) as are Kodiaks (again 2 initial attacks + the chain attack).
Juggernauts hurt with the boosted ice axe but you're unlikely to have
much focus to allocate to buying more attacks or charging. Focus hungry 'jacks like
the Decimator or the Grolar should be avoided because you won't have
the focus to buy extra attacks. He also has problems with scenario
play, because his army of 'jacks tends to be bunched up due to his small
control area so challenging objectives can be tricky.
And always take a War dog with him. At DEF 12 he's very easy to hit, bumping it up to DEF 14 means your opponent will have to commit to taking him down. The dog also makes him immune to backstrikes, so he won't have to worry so much after his powerslide manoeuvre.