I'd seen it before on a mission but it was a timed extraction VIP capture mission so I just legged it to the pick-up zone without letting any revealed troops get spotted.

Second encounter was a Retaliation mission and I'd handled the other pods without running down my consumables too much so I set an ambush up...

And when half my squad were stunned, disorientated or dead I went away and had a long hard sulk about RNG and the inability to hit with overwatch shots, except when a dodge does just enough damage I'm getting pinions rain down with no chance to avoid them...

Fortunately I wasn't iron manning and a second attempt had some much better overwatch shots, even if neither poison nor frost seemed to slow the Archon King down significantly. It got away, but since it had no armour left, only half its hit points and took a couple more reaction shots as it ran for the portal I'm hopeful it'll be easier to handle next time...