Immediately after the Fall, Eldrad and Harlequins attempt to Close the Portal to Save Astheneia

2500 pts of Craftworld and Harlequins vs 1250 pts of Slaanesh and 1250 pts of Nurgle

The Warp Tear
Single objective at the table center, representing the Warp Tear

Warp Tear begins with 1 Warp Point If the Warp Tear is ever reduced to 0 Warp Points, the portal is sealed, and Eldar immediately win a major victory

The portal can never end a round with more than 3 Warp Points, and it can gain at most 1 Warp Point each round (further warp point additions are lost at the end of the round).

Eldar psykers can remove 1 Warp Point by completing a WC 5+ psychic action when within 6" of the Warp Tear during the psychic phase instead of casting a power, which can be denied just like other powers.

Daemon psykers can add 1 Warp Point by completing a WC 5+ psychic action when within 6" of the Warp Tear during the psychic phase instead of casting a power, which can be denied just like other powers.

Deployment
Both sides collaboratively set up terrain, attempting to make the table look as much like the ruins of a debaucherous Ancient Eldar temple as possible.

Chaos deploys first, placing all units within 12" of the table center, or in strategic reserves for free

Eldar deploy second, placing all units within 12" of any table edge, or in strategic reserves for free

Chaos takes first turn

Strategic Reserves
Any Chaos units in strategic reserves may be deployed anywhere within 12" of the Warp Tear, including within 1" of enemy models, at the end of their movement phase (during the reinforcements step?)

Any Eldar units in strategic reservers may be deployed anywhere within 6" of any table edge, including within 1" of enemy models, at the end of their movement phase (during the reinforcements step)

Sustained Assault
All non-named-character Eldar units, and all Troops-role Chaos units, are automatically returned to a 'sustained assault' pool when they are destroyed.

Those same classes of units may be returned to the 'sustained assault' pool at the end of their movement phase if they have half or fewer models remaining, or half or fewer wounds remaining for single-model units.

At the start of each command phase, roll a dice for each of that side's units in the sustained assault pool:

Eldar Troops units move from the sustained assault pool to strategic reserves on a 3+

Chaos Troops units move from the sustained assault pool to strategic reserves on a 5+

All other non-named-character and non-Troops Eldar units move from the sustained assault pool to strategic reserves on a 5+

Result
With more units returning through sustained assault, the Eldar are likely to seal the Warp Tear by the end of round 5.

If they have NOT sealed the Warp Tear by the end of round 5, then victory is determined by the status of the Exalted Keeper of Secrets:

If the KoS is still on the table, Chaos wins a Major Victory

If not, Eldar win a Minor Victory.