Kristoff Erbe is a Knight of the Sphere but has only average stats for a heavy 'mech. However, Kristoff does show two particularly useful traits: Jump Jets early on the main dial for maneuverability, and a relatively forgiving (for a heavy 'mech) heat dial. He has a reasonably attractive, if somewhat spindly, sculpt with a pleasant paint job similar to the other Knights of the Sphere. This unit will be most attractive for those who play faction-pure Republic of the Sphere, as it fills the heavy 'mech niche nicely albeit at a premium price.
Kristoff doesn't have any flashy, high value stats. Other than his aforementioned easy heat dial, he's a pretty normal heavy 'mech with decent range and punch. Very late in his dial he picks up Improved Targeting, which could give your opponent a nasty surprise in the closing stages of a battle. He's a trifle expensive for what you get, so you'll want to use him mostly in higher point-total games (500 pts and up).
Strategies and game play:
Not many heavy 'mechs have Jump Jets, so you may be able to catch your opponent off-guard with Kristoff's maneuverability. Given his range, nimbleness, and well-rounded overall character (including advantageously placed repair markers) you should probably be aggressive with him, and push him a little harder than you normally would a heavy. Remember that he picks up Improved Targeting late on the dial, so you'll suddenly get more dangerous just when your opponent would think you are weakening. Use this surprise to your advantage and press home the fight!
Combos with other miniatures:
Kristoff is well-rounded offensively and defensively (a 22 Defense with Heavy Armor). Support him with vehicle and infantry screeners as you would any 'mech.
Ways to counteract it:
Given Kristoff's range, your best bet would be to lay down artillery fire to wear him down while he's still out of range of your other units. As he closes in, duel at range with a long-ranged 'mech or vehicle equipped with Hardened Armor and Armor Piercing special equipment. Once he gets in close, try to stay inside three inches so that his main guns (minimum range of 3 inches) can't target you. Use units with Streak Missiles to hit him from behind cover, but be wary of his Jump Jets!
Has Jump Jets early for maneuverability, and Improved Targeting later for a late-game surprise. Has a fairly easy, forgiving heat dial with only minor heat effects and minimal modifiers.
Expensive for what you get.
Artwork and aesthetics:
The sculpt is relatively decent compared to some other renditions of the "unseen," and the paint job is pretty nice for cheap sweatshop labor. The color scheme is an oddly pleasing black and navy combination, with realistic mud on the feet and lower legs.
I give this figure an overall rating of 6 out of 10. A solid 'mech with some interesting traits, but expensive.