I picked out the four record attachments as the best designed cards for the mono-sphere archetype the designers were trying to push during the Against the Shadow cycle. What's so well designed about them, you may ask? Well, for one thing they're not absolutely exclusive - you can play them outside of mono-sphere, but for a higher cost. This makes sense for the setup, because it means that the powerful effect is generally available, but is more easily accessible to someone who chooses to focus on one sphere only rather than blending them together. Furthermore, it provides mono-sphere in particular with access to an effect which is likely more useful for them than it is for dual or tri-sphere setups, because a mono-sphere deck is likely to have a wider variety of events it may wish to recur in its chosen sphere, while a multi-sphere deck will have a mixture from multiple spheres. Which leads us onto the design of the cards themselves - they give tremendous flexibility since they allow you to choose any event in your discard pile at the moment you choose to discard the record - so long as it's an action not a response - in contrast to other recursion effects which would have you choose a specific card to return to hand or shuffle back into your deck. Moving the event subsequently to the bottom of your deck neatly limits the recursion (so multiple copies of the record or attachment recursion won't allow you to immediately recur the same copy of an event multiple times), but in turn allows for additional recursion if you have enough draw or fetch effects to retrieve the event from the bottom of your deck. And then there's just the general uses of recursion - it works for playing events multiple times, but it also works very well for any strategy which involves discarding a lot of cards (such as Noldor or Caldara) since with a record in play it's like every (non-response) event in your discard pile is in your hand. Between the flexibility, the power of recursion and enabling some different playstyles for mono-sphere in terms of your attitude to your discard pile, I'd say it's hard to argue the records aren't incredibly well designed. All that remains is to examine the sphere-specific aspects of each record.
So the Scroll of Isildur in . Mono- to me tends to be much more a multiplayer thing, 3-4 players rather than 1-2, though there are exceptions. Certainly I've made great situational use of the ability to recycle Advance Warning, when paired with a Dúnhere deck, and a similar principle could apply to Haldir of Lórien, Great Yew Bow or Forth Eorlingas! For more widespread use though, I'd say the obvious options are to mess with the encounter deck/staging area and draw cards. For the former, the ability to recycle Secret Paths or Radagast's Cunning can add some security to questing, as can The Evening Star, while repeat use of Gildor's Counsel just makes it easier and if you can afford it (possibly with Secrecy), recurring Out of the Wild to pull all of the encounter deck's teeth is a potent option to have. On the card draw side, a mono- deck can run itself incredibly fast with multiple uses of Daeron's Runes, Mithrandir's Advice, and even Peace, and Thought, but it can also help someone else or everyone by bringing back Heed the Dream or Deep Knowledge. I think those cover all the main options, but some of the other events, much like Advance Warning, can be incredibly powerful if used and reused in the right context. I'll just add as one last point that of course you can also return the Scroll to your hand after use with an Erebor Hammersmith if you want to recycle more events. None of the options are quite the same level of big bomb effect as the global readying events in , but used right they can smooth out your game no end, making the Scroll an incredibly potent option which it's hard to pass up if you're playing a mono- deck.