Mirage: Arcane Warfare is a spiritual successor to Chivalry: Medieval Warfare, though with the semi-realistic setting replaced with bizarre characters and plenty of destructive magic. However, the biggest difference between Chivalry and Mirage lies not in the setting, but rather in the characters themselves. You don't get to pick and choose your favorite weapons like you would in Chivalry, but instead you have to select from a variety of characters that come with their own predefined skills, weapons, and magical abilities.
Since all of this is hard to grasp through words alone, allow me to show you the recently posted gameplay preview. Its a fairly lengthy video, totaling at around 11 minutes, so it should give you a damn good idea of what Mirage is all about. Have a look:
As for the closed beta, it will allow you to play six character classes with two tiers of unlockable abilities, mess around on eleven maps, and see what Mirage's five game modes have to offer. The beta sign-ups are unfortunately no longer available, but if you are interested you can secure yourself a slot by pre-ordering Mirage on Steam for €28. As an added bonus, if you already own Chivalry: Medieval Warfare you will be given a 10% discount. Its not much, but its the thought that counts I suppose.
To learn more about Mirage, or just check out a whole bunch of gameplay videos, I would suggest heading over to the official website. And as a final note, here's a breakdown of all the beta content: