Have you seen those chests in the Iron Keep? The ones on lava? They're impossible to reach without the fire-resistant Alonne Knight or Alonne Captain set, nabbed off the area's titular enemies. Combine this with the Flame Quartz Ring, a Small Orange Burr consumable, a Lifegem to slowly regenerate health, and the pyromancy spell Flash Sweat. Finally, either use the Pharros' Contraption in the vicinity to unleash water, or break any nearby jugs, then roll in it. Even after all this, you're still not immune, but it's just enough to reach the first chest containing a Phoenix Parma shield, and the second containing the Chaos Storm pyromancy.
Dress like the enemy
Fancy fooling online opponents by dressing like AI? Farm the Hollow Solider Helm, armour, gauntlets and leggings off Hollow Royal Soldiers in the Forest of Fallen Giants, then grab an appropriate weapon like a halberd, bastard sword, estoc or longsword. Nobody will know the difference! This works on any enemy whose armour you can farm - Alonne Knights in the Iron Keep or Archdrakes in the Shrine of Amana, for instance. Make sure to kill an enemy then stand sentry in his spot until your opponent arrives for added deception.
Dress like a phantom
You can also fool players who summon you as an invader into thinking you're a friendly phantom instead. Slap on the White Ring and you'll glow with a deceitful white aura. I've paired it with the Leydia White Robe and Grave Warden Mask for a ghostly touch. Trade with Dyna and Tillo in Things Betwixt for the ring. As for the robe and mask, farm Leydia Apostles in the Undead Crypt and Grave Wardens in Earthen Peak.
One-off armour pieces
Most armour comes in sets consisting of head, arms, legs and torso, but one-off specialties exist. Find this Singer's Dress in the Shrine of Amana by going to the third bonfire and heading back towards the second while keeping to your right. It's hidden in the cliff wall behind some breakable roots. An ogre guards it, and he's particularly tasty in the water, so bait him out and rush past him if you don't feel like having your head chomped on
My Engraved Gauntlets are found in a room in Brightstone Cove Tseldora, accessed using the Tseldora Den Key. This key is received after saving either Mild Mannered Pate or Creighton the Wanderer when they have a scrap in the same location (you must exhaust all their dialogue options for this to happen). Finally, there's Durgo's Hat (an ultra-rare drop from invaders at the King's Gate bonfire in Drangelic Castle, provided you've used an ascetic), the Red Lion Warrior Cape (drops from Red Lion Warriors in the Shaded Ruins), and the Flying Feline Boots.
Become a pot
Use a Silver Talisman consumable to transform into an object. It's contextual, so in one area you might look like an aged vase, and in another a rock, or a crate, or even a painting. Sorcerers can cast the Chameleon spell for the same effect. You can actually block while transformed, as long as your guard doesn't break. I've got those dragons fooled.
And that's as much as I've mustered so far. What's your favourite armour set from Dark Souls 2?