Basically it would be similar to Arena levels in the clockworks. You'd get stuck in a danger-room style area, either alone or with a team of 4, and have to fight off waves of regular clockworks monsters.
The catch is that another team is also doing the same fight right next to you at the same time, and you score points by completing waves faster, losing fewer hearts, needing fewer revives etc. At the end, say after clearing 3 rooms, the team with more points gets the 280cr, krog tokens, and so forth.
Like LD, it would have the regular T1/T2/T3 split so you aren't going up against teams remarkably better equipped than you, nor against monsters that are going to completely clean your clock.
Given that very small matches would be viable, even 1v1, it would be nice to be able to form your own custom match and invite players of your choice to compete with or against.
Unbalanced teams would also be possible (like, say, 4v3) by using the regular clockworks HP scaling for the monsters on each side respectively.
How will monsters be chosen? it may end up being a matter of how lucky you were choosing weapons and armor.