Disclaimers:
Although the seal pertains to "raids" in-game, the triumphs required to complete it can only be done in the Last Wish raid. Additionally, this is not meant as a guide on how to complete the Last Wish raid. If you are looking for resources on the raid and its encounters, a comprehensive guide can be found here. This guide will be focusing on the triumphs themselves. Finally, this guide will obviously contain spoilers for the raid, so if you have yet to complete it or don't want it spoiled, I don't recommend reading.

For those seeking to earn the title, here are a few things to note going into it. First and foremost, if you are unfamiliar with the process of unlocking a seal, here's what you need to know.

Triumph seals are located at the bottom of the triumphs page in the player menu. The Rivensbane seal is located on the second page of seals, to the right of the immediately displayed ones. To complete a seal, you must complete and claim all of the seal's associated triumphs. You can see what triumphs are required/completed in-game by clicking on the seal on this page. Note that this seal has two pages of triumphs.

The second thing to note is that some of the triumphs involved in getting the seal are time gated. In other words, you will need five weeks minimum to complete every triumph as the five individual encounter challenges are on a weekly rotation. Finally, you will need to complete a collections badge (specifically, the Raid: Last Wish badge) on at least one character as part of the seal requirements. This badge can be found on the second page of badges shown in the collections page in the player menu.


Almost the entirety of the set of items you will need to complete this badge come from randomized loot drops throughout the raid. Some of these items come from much rarer or limited drops than others, meaning that you may need to complete the raid many times to obtain them all. TL;DR: A portion of this seal is RNG/luck-based, unfortunately.

This guide will be organized into a few sections to go over the 16 different triumphs and how to complete them. I have categorized them from most straightforward/easy to most complex/difficult.

Overview
These triumphs are the "simple" ones, simply requiring raid completions or other small tasks.
1. O Murderer Mine
Requirement: Complete the "Last Wish" raid.
This triumph is pretty straightforward. All you need to do is complete the raid once.
2. Clan Night: Last Wish
Requirement: Complete the "Last Wish" raid with a full fireteam of clanmates.
To complete this triumph, everyone in your fireteam must be in the same clan when the raid is completed.

3. Put a Flag On It
Requirement: Plant 5 "Last Wish" Raid Banners.
To complete this triumph, you will need to plant raid banners at least five times. It does not matter at which encounter you plant a raid banner, you just need to do it five times. For those who don't know what raid banners are or how they work, a raid banner is a consumable item you can purchase from Suraya Hawthorne in the Tower or from Petra Venj in the Dreaming City. To plant one, before the start of any encounter in the raid, you should see a white circle on the floor. Stand in the circle and hold your interact key to plant a raid banner if you have any in your inventory. (Tip: Once a raid banner has been planted, you can hold your interact key near it to rally, fully charging your abilities and fully refilling your ammo. You can only rally once before an encounter starts.)
4. Treasure Trove
Requirement: Loot hidden chests in the "Last Wish" raid 10 times.
There are two "hidden" chests in the raid. One is located between the Kalli and Shuro Chi encounters, and the other is located between the Shuro Chi and Morgeth encounters.
5. Habitual Wisher
Requirement: Make 10 wishes in the "Last Wish" raid.
To complete this triumph, you will need to use the Wall of Wishes to make 10 different wishes. A full guide on the Wall of Wishes can be found here.

Overview
These triumphs are also pretty straightforward. Each one involves completing raid encounters with a fireteam of either all the same Guardian class or subclass. As such, one key thing to note is that none of these triumphs require being locked into a class or subclass for a whole run. For example, it is entirely possible to do the first three encounters with a full fireteam of solar subclasses in one run, then do another run in which the last three encounters are completed with every fireteam member using a solar subclass. You can even do these one at a time.

6. Thunderstruck
Requirement: Complete all raid encounters with a fireteam made entirely of Arc subclasses.
Every fireteam member must be using an Arc subclass at the end of each encounter.
7. Sunburn
Requirement: Complete all raid encounters with a fireteam made entirely of Solar subclasses.
Every fireteam member must be using a Solar subclass at the end of each encounter.
8. Night Owl
Requirement: Complete all raid encounters with a fireteam made entirely of Void subclasses.
Every fireteam member must be using a Void subclass at the end of each encounter.

For these three triumphs, each encounter simply has to end with every fireteam member using the same elemental subclass. This means you can have players switch to the necessary subclass before the encounter ends to fulfill the requirement.(Edit: This no longer works, so be sure to begin and end the encounter on the correct subclass.)

9. The New Meta
Requirement: Complete all raid encounters with a fireteam made entirely of the same Guardian class.
Every fireteam member must belong to the same class at the end of each encounter (i.e. Hunter, Warlock, Titan). For this triumph I recommended completing one run in which every fireteam member belongs to the same class, as switching characters mid-run (or mid-encounter) can be inconvenient. However, you can still complete this triumph one encounter at a time as with the others above. Additionally, you and your fireteam do not have to use the same class for an entire run, so if you find some encounters easier for different classes, you can use whatever class suits your fireteam best.

Overview:
This is where the requirements start to get more complicated. Every encounter in this raid (except for Queenswalk, or delivering the heart after beating Riven), has a challenge. For any challenge to count as "completed", you will need to pick up its "Weekly Raid Challenge" bounty from Suraya Hawthorne in the Tower, then complete the encounter's challenge. Note that only one encounter's challenge bounty is active per weekly reset, meaning you will need to complete each challenge over five separate weeks. Additionally, the active challenge every week cycles through the five encounters in order, so if one week's challenge is Morgeth, the next week's challenge will be Vault, etc. You absolutely do not want to miss a week's challenge, as otherwise you will have to wait another few weeks for it to be available again. Finally, understand that the challenges may force you to change how you approach an encounter in order to complete them successfully. If you fail a challenge during the week it is active, you will see the text "Challenge Failed" appear in the lower left corner of your screen. If you complete a challenge during the week it is active (and currently have the bounty), you will see the "Bounty Completed" notification appear on the right of your screen. To unlock the triumph, simply open your Director, go to the Quests tab, and collect the bounty as with all others. (Note that if you fail a challenge, you can simply have everyone wipe and try again.)

Update Post Season 17
Weekly challenges for Last Wish are no longer tied to the old bounty system, but to the modifiers which change weekly (in line with current/newer raids). On the weeks which feature Last Wish as the legacy (pinnacle) raid, all challenges are active and can be completed for rewards/triumphs.

10. Summoning Ritual
Requirement: Complete the Summoning Ritual challenge.
This is the challenge for the Kalli encounter. To complete the challenge, before each damage phase, all nine plates must be defused/activated. Additionally, each "wrong" plate containing a symbol not shown in the middle of the arena will summon an ogre when activated. These ogres must be killed. If your fireteam does not manage to kill Kalli in one damage phase, simply repeat the process of defusing/activating each plate and killing all the ogres before damage phase until the encounter ends.

11. Coliseum Champion
Requirement: Complete the Coliseum Champion challenge.
This is the challenge for the Shuro Chi encounter. (Note: The bounty from Hawthorne for this challenge is titled "Which Witch," but the triumph is titled "Coliseum Champion," so don't be confused.) To complete the challenge, no members of your fireteam can be hit by Shuro Chi's projectiles (her shouts are fine) during the encounter. Shuro Chi will fire the projectiles before each individual damage phase, and will stop once your fireteam has cleared the adds and spawned the laser prisms for that phase (this will also show the text "Shuro Chi's tempo quickens").
Without going too deeply into any strategies here, I will note that to be best equipped to complete this challenge, you and your fireteam should know where cover spots are to avoid being hit. I have also heard that having the projectile hit a Titan barricade or Ward of Dawn (bubble) can fail the challenge, so keep that in mind. Finally, sword blocking the projectiles will not fail the challenge, so you may want to consider equipping and using a sword for that reason.

12. Forever Fight
Requirement: Complete the Forever Fight challenge.
This is the challenge for the Morgeth encounter. To complete the challenge, the ogres Morgeth spawns must not be killed... That's it. Kill Morgeth and leave the other ogres alive.

13. Keep Out
Requirement: Complete the Keep Out challenge.
This is the challenge for the Vault encounter. To complete the challenge, the Knights (Might of Riven) that spawn in the three rooms cannot be allowed to ever leave the rooms; they must be killed before exiting. You'll want to have add clearers stay inside the rooms even while locked so that getting to and killing the Knights isn't a problem. A common strategy for this encounter involves using Tractor Cannon to slow the Knights' momentum and weaken them so they can be finished faster.

14. Strength of Memory
Requirement: Complete the Strength of Memory challenge.
This is the challenge for the Riven encounter. To complete the challenge, no player can shoot the same eye (Riven's eye, not the taken captain enemy) more than once. Note that it is possible to complete the challenge simply by doing the Riven cheese, as no eyes are ever shot when doing this.

15. Petra's Run
Requirement: Complete the Petra's Run version of the "Last Wish" raid.
To complete this triumph, you will need to complete a successful Petra's Run. Petra's Run is a version of Last Wish in which you and your fireteam must complete the entirety of the raid with no deaths. Not one. Upon a fireteam member dying for any reason, the fireteam will be returned to orbit and the Petra's Run will have failed.
Petra's Run must first be activated by entering its wish (Wish 13) into the Wall of Wishes. Until the wish has been entered, fireteam members may die without failing the run. Once activated, no player can die. When in a Petra's Run, keep in mind doing any of these will fail the challenge:

• Dying
  
• Blowing yourself up
  
• "Physicsing" yourself to death (in other words, having Tractor Cannon backfire and pushing yourself into a wall and dying, or Worldline skating into a wall, etc.)
  
• Dying
  
• Falling off the edge in any platforming section, including between encounters.
  
• Cleansing the wrong plate in the Vault encounter
  
• Dying
  
• Picking up three Taken Strength
  
• Failing to get into a room when Kalli performs her wipe mechanic
  
• Dying
  
• Shoulder charging your friend off the edge when they get up to grab a snack

With this in mind, you are now fully prepared to attempt this challenge. But seriously, there are plenty of guides, strategies, and knowledgeable players out there to help you with completing a Petra's Run. My biggest tip is to be comfortable with all the raid mechanics, be flexible in any encounter, and stay calm throughout the run.

16. Complete the Raid: Last Wish Collections Badge.
Because this isn't a triumph, it will be marked complete once at least one character has everything listed in the badge. As stated before, completing the collections badge is almost entirely dependent on luck. The most efficient way to obtain every item listed is to simply play through the entire raid, completing all encounters, once a week on three different characters, looting both hidden chests during the raid. Enough of this will eventually net you the various raid-exclusive weapons and armor. The other items are as follows:

• Wish No More: An emblem you receive upon completing the raid for the first time.
  
• Dreaming Spectrum: A shader you receive upon dismantling a curated (set roll + fully masterworked) weapon that can randomly drop after completing an encounter.
  
• Wish-Maker Shell: A ghost shell that randomly drops after completing either the Kalli encounter, the Shuro Chi encounter, or the Vault encounter.
  
• Cleansing Knife: A sparrow that randomly drops after completing the Morgeth encounter.
  
• Ermine TAC-717: A ship that you must acquire from an additional chest between Morgeth and Vault. This chest must be spawned in using Wish 2 on the Wall of Wishes. You can only open this chest with a Glittering Key, a random drop from one of the chests at the end of the raid.
  
• One Thousand Voices: An exotic fusion rifle that randomly drops from one of the chests at the end of the raid.

To help your chances at obtaining either the Glittering Key or One Thousand Voices, you can use Wish 1 on the Wall of Wishes. This will give you an extra Ethereal Key to open one of the chests at the end of the raid, but only once per character ever. I will state once more that this badge involves a fair amount of RNG, so fully completing it may take a while. Good luck!

Once you have completed every requirement listed above, make sure you have claimed all your triumphs, and you will have finished the seal. To equip it and show your Rivensbane title to everyone else, open the contents of the seal and click on the Rivensbane title in the lower-left corner to equip it.
If you've managed to either complete the seal (or read through this whole guide) then congratulations! If you have any questions or feedback relating to the guide leave them in the comments below. Hopefully this helps!