Wyrmius is a mini-game in Warframe. To get access to Wyrmius, you will need to purchase the Ludoplex from Cephalon Simaris. This will cost you 50000 Standing. You will then need to buy the Wyrmius mini-game from Simaris for 25000 Standing.
If you own the Wyrm or Wyrm Prime Sentinels, you can play the game by going to their Appearance tab in the loadout screen and click on the W loadout.
You can earn Standing with Cephalon Simaris by finished daily bounty challenges. To get these, you need to visit Cephalon Simaris on any Relay, and he will give you a synthesis target to track down and scan. You will also earn a small amount of Standing each time you scan any enemy during a game.
When you purchase the Ludoplex from Cephalon Simaris, you then need to place it in the Orbiter as a decoration. Open your main menu, then go to the Equipment, Orbiter, and choose the option to decorate the Orbiter. Find the Ludoplex and then place it where you like in your Orbiter. Interact with the device and select Wyrmius from the options.
Wyrmius plays out like a side-scrolling bullet hell shooter. You control Wyrm, and you need to destroy waves of enemies that come at you. Some of them will drop powerups that will alter your weapon in various ways. You have three lives, and when you lose them all it is game over.