Here are some tricks for unveiling rivens.
- If you have to kill Dargyn pilots before they hit the ground, pilots who were on the ground, and are lifted by a warframe's abilities count. These abilities inclued Rhino's Stomp, and Titania's Spellbind. Also, if you shoot down a Dargyn, the pilot has a decent chance to survive, so you can hunt them down after they land, lift them up, and then kill them and have it count.
- If you need to shoot down Dargyns with a bow, equip a bow as your primary weapon, then go to the Plains of Eidolon. Go into archwing, and hunt Dargyns. You can fly right up to them and shoot them, and have it count. Note that shooting Dargyns from the rear has a chance to kill the pilot instead of the Dargyn itself, so for best results, shoot at them from the side or front.
- If you need to get some number of headshots, equip a weapon with a fast rate of fire, like a Soma. Go to the Plains of Eidolon at night, and find the Eidolon (the big screaming thing). Shoot it in the head a lot. That won't kill it, but it will satisfy the conditions of the riven. It'll also make the Eidolon mad, so you should retreat after shooting it. Alternatively, shoot a vomvalyst. All shots on it count as headshots.
- If you need to get more than one headshot in a single aim glide, take the arca plasmor, go to a low level defense with Loki. Use radial disarm on a bunch of enemies, then go invisible. They'll cluster around the defense target. Jump and shoot just over their heads. If you're lucky, that should do it. It may take a couple of tries but it usually works before I get to round 5.
- If a riven mod involves scanning a Simaris target without using abilities, that means without using abilities on the target. You can still do the challenge with invisible Ivara, and scan the target without spooking it.
- If a mod requires you to do a task without taking damage, use Rhino's Iron Skin. Damage taken by Iron Skin doesn't count. There's an augment for Rhino which lets you detonate and recast Iron Skin, if it's getting low.
- If you have to get killing blows on some number of sentients, hit the plains at night. Vomvalists count, they're plentiful, and if you have an amp, they're easy to kill.
- If you have to get a certain number of kills without setting off an alarm... the bad news is, the count resets whenever an alarm is raised on the mission you're in, and you have to start over. The good news is, there are plenty of places where they don't raise alarms... the open-world areas and the Void.