Risk of Rain 2

Before attempting this achievement, you'll want to make sure you have at least 15 Lunar Coins, to be safe. Lunar Coins have an incredibly small chance to drop from enemies, but you'll assuredly find some across all your runs. However, the two guaranteed ways to get Lunar Coins are:
 

• You get five Lunar Coins from obliterating yourself at the Obelisk. Refer to True Respite (30G) for how to do that. 
• You get ten Lunar Coins for beating the game. Beating the game isn't required for any achievements, but if you take the teleporter to the moon from Sky Meadow, which is its defeat location, you can go through the steps there to fight the final boss and then escape on your ship, beating the game and being rewarded with ten Lunar Coins. 

Either way, once you have at least 15 Lunar Coins, you can get this achievement in one or, at most, two stages. What you need to do is, in Stage 1, find the Newt Altar in it, pay a Lunar Coin to it, finish the teleporter event, then hop in the portal to be taken to the Bazaar Beyond Time. Head into the shop, and on the left are five Lunar items for two Lunar Coins each. If you have ten Lunar Coins you can obviously buy all five, but the problem is that some of them are items (meaning you can hold and stack as many as you want) and some might be Lunar equipment. Since you can only have one equipment equipped at a time, if, of those five Lunar items for sale, more than one is an equipment item, you won't get five in a single trip to the Bazaar. You should get a solid three items though, and one equipment. This gives you four of the five you need for this achievement. If you get all five, great, but if not, you need to do the same thing on Stage 2: find its Newt Altar, pay a Lunar Coin, take the portal to the Bazaar, and buy however many more items you need. 

Refer to Newtist (20G) for the locations of all Newt Altars.