My way

 Oltauron looked at his stout fellows. Splendid in their black and silver armour, the Dark Reapers had been issued a fire support position to the right of the main battle line. Oltauron and his four fellows had been summoned from the main battle line by the Phoenix Lord Maugan Ra, the Harvester of Souls in order to secure the Chaos Idol before the approaching Orks could seize it. 
Along was two units of 10 Dire Avengers, one unit of 20 Storm Guardians and 10 ancient warriors in the form of Wraith Guards. The plan was to form a seemingly weak battleline with the storm troopers in the vicinity of the Idol, and then to charge and tie down the main Ork battleline while peppering them with Shuriken Catapults and the heavy missiles from the Reaper launchers.
Maugan Ra took the left flank himself so as to ensure that everybody worked according to plan, and put the venerable ones to the right.

With the usual immense noise and dust clouds, Oltauron could feel, hear and see the Orks approach. Just as the Harvester of Souls had predicted, the Orks put up two hordes of Boyz in the centre, and one horde of Truck boyz on the Ork left flank. This was going to be a turkey shoot, and Oltauron smiled inside his helmet.

An immense roar emmited from the Ork battleline as the Boys fell into line, not a sound was heard from the Eldar line.

Suddenly the Venerable Ones lumbered forward, the Spiritseer calling over the Coms "Main Battle Tank sighted. Engaing." Apparently a Leman Russ Demolisher had been captured and pressed into service on the Ork side. In order to to get clear line of sight on the main battle tank, Oltaurons squad was told to destroy the truck immediately in front of it. Switching to AP, the squad unleashed a string of missiles towards the truck most to the right, and with 6 impacts on the front armour, the truck was doomed. One of the missiles struck the gastank, and the vehicle turned from a threat to an Ork entangled burning wreck. "Visual" was the only message from the Venerable ones, as they front trooper activated the wraithcannon. In the moment the trooper engaged the trigger, he was momentarily distracted by the Boss wagon just left of the target, and thus the ball of nill-space materialised inside the crew compartment and thus stunned the crew instead of outright destroying the main battle tank.

Maugan Ra had at the same time exploded 3 orks with the Maugetar. This prompted the Orks into action. The non-coordinated forward surge from the main horde stopped exactly where predicted, and when the warboss's truck charged the Venerable ones, Oltauron had to restrain himself in order not to cry out in triumf. 
The joy was however shortlived, as the far forest edge was lit by three explosions. "Incoming" was shouted on the radio, but at that time it was too late. Three stormtroopers and on Venerable One had been killed. Unfortunately, the shock of the explosion was such that the storm troopers went into cover and refused to stick their heads out again. With usual Ork ruthlessness, the artillery shells had been put right in front of the now fast approaching truck boys and slugga boyz with the War boss, and in the confusion of the shells Oltauron was appaled to see three Venerable Ones be slaughtered in the onslaught before they themselves could retaliate.

Deprived of the support of the stormguardians, Maugan Ra ordered the Avengers forward and for them as well as Oltaurons squad to concentrate all fire on the left of the main hordes. Oltauron slaved his targetting to the Exarch of the right Avenger unit so as to avoid multiple hits on enemies, and relayed to his fellow Reapers. Unfortunately, this Exarch was left/right confused, and so chose to fire all guns on the light goblin screen in front of the main line. As the last goblin was in front of the right horde, and not the left, Oltaurons squad unleashed on this horde instead of the original target. This had the unfortunate effect of confusing the other Avenger unit so badly, that only three orks were destroyed. If only the stormguardians could counterattack, but they seemed eager to continue hugging the ground. Desperate times calls for desperate measures, and so the venerable ones were ordered to charge back. Oltauron could see no point in this until the shadows seemed to solifidy around slender checker-suit dressed eldar: Harlequins! These elite close combat troopers assaulted the Ork warboss and his boyz, and in a blink of an eye annihilated them. The other ork unit was called back in order to relocate, thus sparing them the same fate. The Harlequin disappeared into the shadows once more.

With utter contempt for troops who hide, the orks chose to ignore the stormtroops in order to fire directly into the Avengers, and the sheer number og bullits that flew killed ten of these noble warriors. Somehow two Venerable ones were killed too, probably from the Ork artillery that seemed to hit whatever it was targetting. Facing devastation if the storm troopers kept hiding, Maugan Ra invoked an ancient battle hymn, and just in time was the order restored among the stormtroopers. Just in time too, as the Orks hit the main defensive line, and such was the ferocity of the assault that not a single of the storm troopers was left standing. What was worse though, the resistance that was put up was so feeble, that the orks had momentum enough to engage the Avengers. Unfortunately this meant that Maugan Ra was caught up in the combat as well, with almost 25 orks swarming him, thus dividing his attention between personal survival and the battle. 

Time had come for the Harlequin to reappear and charge the now close combat swirling orks that had engaged the Avengers. Oltaurons squad had at this time located the gun battery, and laid down a barrage of missiles in the forested area, unfortunately without hitting a single gun. The Venerable ones moved to intercept the Leman Russ main battle tank, but due to mutual respect of the units, the distance was too great for the guns to be effective. Almost on cue, the Harlequin appeared, and annihilated the first 17 orks, fully expecting the Avengers to slaughter the remaining orks. Unfortunately, the Avengers proved to be shaken, apparently so shaken that the 12 remaing orks chose to fight on. Under the weight of so many orks, Maugan Ra had to give in, and a wellplaced chop to the neck momentarily took the ancient warrior out.

Despair was now apparent, but the Harlequin was still in the thick of it. Maybe victory could still be snatched from the jaws of death. Seeing the lack of combat will in the Avengers, the Troupe Master chose to keep the Harlequins in the battle so as the Avengers could disengage. Unfortunately, a truck full of truckboyz was able to support an assault directly in the back of the Harlequins. Now outnumbered 4 to 1, the Harlequins took out 17 orks before succumbing to the inevitable. Short process was made of the remaining Avengers, and Oltauron called out for emergency assistance from HQ as he reloaded with HE. Now almost 40 orks were charging his position, and as the last Venerable one took out another Ork before crumbling, Oltauron could see the orks take out the long heavy swords called choppas and ready for the charge. He issued the order to set the ammunition to self destruct upon lack of vital signs, and shot again into the face of a particular large ork. "Help on the way. Strike Force Falcon with the titan Glory of the Asurmen of the way. ETA 3 minuttes". As he heard the explosions sound, one, two, three and four, Oltauron replied on the main coms net with a single word: "Bugger".