Tainted Grail: Conquest

The First Guardian is the encounter marked "Legendary Encounter" in the first area of Wyrd and takes the form of a Stone Golem. The Golem has a deep health pool and has a variety of attacks, so you will need some way to avoid damage (Blocking, Summoner Golems, Barrier etc) to be able to last. Whenever you deal a certain amount of damage, or use a Stun type effect on the golem, it will summon an ally with HP proportional to the amount the golem has lost. Whenever one of these allies is killed, you will gain a White card that allows you to attack the Golem for 0 Energy. There are also "Risk" and "Gamble" cards that will give you a point of Block and 1 extra Energy, or allow you to Stun the Golem to avoid damage, but using either of these will lose you 10 Armour per time (i.e. you take 10% more damage from every attack for the rest of the battle).

I find the fight easiest with the Summoner class, using the Golem starting minion Passive Skill. Keep a Barrier active at all times, if you have spare energy and Barrier cards, use them. Otherwise, focus on summoning a Wyrm as your second minion. Promote the Wyrm as much as you can, using activations mainly on it, unless the Golem needs to heal. If you lose your Golem, summon another ASAP. As the battle goes on, the Wyrm will deal more and more damage, as well as lowering the Golem's Armour, which makes it more vulnerable to everything. Good Sigil type cards to grab are Oversaturation, Revival, Existence (a 0 Energy card, which makes it incredibly useful) and Self Awareness. Balance keeping your Golem alive, a Barrier on the Summoner and dealing damage with the Wyrm. Avoid using Risk or Gamble Cards, unless you think them absolutely necessary.