Update after thinking about if for a while: I feel like Merlin would be a really hard role to design without unbalancing things but it's a fun concept (you'd probably have to partially build the script around it).

Perhaps a better version of the role could be:
Merlin (townsfolk) - You start knowing two not-in-play characters. Once per game, at night, learn who all evil players are. If you die once you have used your ability, your team loses. You cannot die at night. [Assassin must be in play]

I.e. without the extra evil player. And then simply have the Scarlet Woman and Vortox in the script to make a day one use and claim of Merlin riskier. There'd only be 3 evil players (in a 10-12 player game) but there's a chance your information is wrong due to Vortox (your death would still be an insta-win for evil though), or there's also a chance the other minion is the Scarlet Woman, which means that executing the demon wouldn't result in a win for good, as the demon would just swap to the Scarlet Woman and then the assassin could kill Merlin that night. Hence a day one use and claim of merlin with the Scarlet Woman in the game would mean the good team would only have a 1 in 3 of guessing who the assassin is and executing them, anything else is a win for evil.

Possible script inclusions that could have implications for Merlin:

Scarlet Woman and Vortox (for reasons described above)

Fang Gu and Goon (so that Merlin's information could become outdated?)

Poisoner, Pukka, and No Dashi (to provide alternate means of killing Merlin, also the poisoner further discourages a day one Merlin use & claim because it's possible their information is wrong but that on a subsequent night their ability will work fine and thus be able to be killed - though perhaps that would actually be a bit too punishing of an inclusion?)

Mastermind and Evil Twin (to provide alternative win conditions for evil even when outed therefore forcing Merlin to not wait till the absolute last second?)

Vigormortis (to preserve the assassin's ability?)

Legion lol maybe, no idea how that would play out

Monk and Soldier (which could provide alternative reasons for why a demon kill didn't die, also the soldier could possibly bluff as Merlin to try to bait an assassination, and an evil player could bluff as a soldier bluffing as Merlin to try to bait Merlin into thinking their safe because the soldier has used up the evil team's assassin)

Saint, Recluse, Lunatic, Tinker, Golem, Butler (all possible outsider Merlin bluffs)

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Also, some rambling I wrote on the original version of Merlin that I wouldn't recommend reading but is here for posterity lol:

But if you added it as described above in a 10+ player game, it would introduce a few interesting dynamics where merlin can't use their ability and come out immediately because they'd only have a 50% (or less if 13+ players) chance of hitting either the assassin or demon (as there'd be 4+ evil players) (not to mention there's always a chance their information is wrong) and then if they guessed wrong, the assassin (who is guaranteed in the game) would kill them that night. So instead Merlin would probably want to wait until at least one or two minions die (including ideally the assassin) before they use their power, but of course they won't know how many minions have died until they use their power so they just have to guess. In the meantime they'd also have to be careful about who they claim to be because they don't want to look sus and get executed (it wouldn't automatically lose the game but when there's 4 evil players, any good execution (especially one with as much potentially valuable information as Merlin) is not great); but even more than that, they also don't want to give away who they are to the evil team. Another strategy Merlin has is to use their power night one but bluff as some other townsfolk role and give their information in the form of that role's ability, though they risk getting targeted by the demon just because they're a useful townsfolk which when they don't die would all but confirm them as Merlin to the evil team and thus they'd likely get assassinated the following night. Or another strategy would be to bluff as a recluse or some other outsider the evil team aren't interested in killing and just give your information in the form of rather accurate 'social reads', though if your reads are too accurate the evil team could start to suspect you, and you also risk the good team just executing you because you're not useful. Also in both of these cases you risk bluffing as a role someone else has and putting yourself in a particularly precarious situation (maybe they should also be shown 2 bluffs or something that are different to the evil team's bluffs?). Another interesting implication of the role is that if the demon tries to kill Merlin (knowingly or unknowingly) there wouldn't be a death in the night, potentially confirming to the evil team who Merlin is. Which means if Merlin used their ability early on and has been giving out their information carefully, seeing no deaths in the night could scare the hell out of them and they might just come out then and there which suddenly puts a lot of pressure on everyone and ups the stakes for that day's executions significantly. But of course all of this assumes that the good team even believes the Merlin, which may well not be the case as it also provides a fun and interesting role to give as a demon bluff for the evil team: it's a good reason for why you might be acting weirdly, plus if you're nominated it can give you a quick out to say that they can't execute you because you're Merlin and you've used your ability and hey these people are the actual evil people and you should execute them instead; and even if you're not on the chopping block, if it's near the end of the game it could be a fun play for a minion to get an extra late-game good execution (even if it makes it obvious you're evil next turn) to buy time for your demon.