Open Strike Hoards
Strike Hoards appear at the end of each Strike in Destiny: Rise of Iron, and these will give you a chance of getting some Strike-specific loot if you have the Skeleton Keys for it. Aside from special weapons and pieces of armor, these chests also have a chance of dropping a Ghost and Artifact – both of which will likely be what you need once you’ve hit the 355 and 365 bottleneck. Don’t be discouraged if you get a blue Artifact instead of Legendary gear; the Artifact will likely be two or three points higher than your current light level, and you can use it to bring your current Artifact level up as well.
The only tricky thing about Strike Hoards is the rarity of Skeleton Key drops and actually getting them so you can open the chests. Bungie has mentioned in their patch notes that Skeleton Keys have a higher drop rate in Heroic Strikes and the Nightfall, so keep that in mind if you’re looking to farm for Keys. They do also drop in the regular Strike playlist, but the drop rate seems to be much lower.