Shamelessly plugged from BoLS...
Scarabs - Fast Attack
Three models in base unit at 45 pts, with up to seven more at 15 pts per model. Fearless, Swarms, Beast, Entropic Strike. Four attacks on the charge with 3+ cover save in terrain (which they ignore for movement purposes - like Harlequins).
Entropic Strike is a new rules accessable to several units in the codex. Against infantry on to-wound rolls of 4+, armor saves are ignored (invulnerables allowed). Against vehicles on armor penetration rolls, each die that rolls a 4+, reduces the vehicle's armor by 1 pt on ALL sides for the rest of the game. Vehicles are destroyed when any of its armor values reach 0.