(Last updated 1/3/2021; v124)
The Ironlights Spectator Client is a 2D PC app that allows you to spectate multiplayer matches of Ironlights. To spectate a match, you must input the private tag for either of the two players.
That means it's perfect for spectating your own matches (e.g. for easier Twitch streaming) or spectating the matches of a friend who shares their private tag with you!