It can also be used to instantly finish crafting items in the Foundry. If the mod you want is from a limited time event (E.G.
There is one activity in the game that will drop a lot of Rare mods though, allowing you to wrap up this challenge in about ten minutes. While this should happen naturally as you play the game, Rare mods do not drop all that often.
The Enhance Challenge in this week's Warframe Nightwave series wants you to get your hands on eight Rare mods.