Rescue! 

Space Marines vs. Eldar

Turn 5:

Storm Lords

Another attack bike appears on the scene, and lends its heavy bolter in a hail of fire against the Wraithlord. This, combined with the sniper rifles of the scouts and the melta gun from retreating tac squad Beta, are enough to down the alien walker once and for all. 

The Devastator Squad opens up with everything it has on the wave serpent, causing the elegant craft to crash into the ground, killing one of its deadly cargo - Striking Scorpions

Tac Squad Alpha, still withdrawing to the rear with the artifact, are provided covering fire by their immobile rhino, which kills another storm guardian, finally breaking the morale of that unit and causing it to flee to the Eldar rear.  They rejoice, as they are within a few yards of safety.

Craftworld Orkan Baharr

Piling out of their damaged craft, the scorpions advance on the withdrawing marines. A withering hail of mandiblaster fire kills a marine as they charge the Monkeigh warriors, and another armored human falls. In retribution, Sergeant Eban kills two of the scorpions with his power sword, and a marine trooper accounts for another. The Eldar, dedicated to their mission,  will not break, and both troops consolidate into combat.

Turn 6