I'd say that's true right up until it gets upcast to 7th level and then it'll work

I think that the immunity to non magical weapons and any spell under level 7 so your spell casters have to be at a higher level

If the threat of the curse changes from setting to setting, if every town and city has clerics and paladins that can heal on the cheap then yeah that is no problem, but if paladins and clerics are rare and far between that makes the curse much more dangerous. A Rakshasa should rarely get into open combat with multiple enemies, they should pull people away from one another turn them on one another through magic and social skills. A Rakshasa "encounter" in a city can easily last days, weeks, or even longer as it sows resentment in the city against the party, secretly attacks the party only to disappear into the crowds to strike again. Mainly if a Rakshasa gets into open combat something has gone terribly wrong for it, and it will want to get out as quickly as possible. It is a slow and extremely careful enemy that the party may not even know it is there until it is to late. 

New DM here, working on creating a world for some friends in which I'm considering using several rakshasa to pose as high nobles that act as master manipulators in a dystopian society. Since they are lawful evil fiends, who originate in the Nine Hells, would it make sense to have them arrive in the world as a unit under the command or contracted employ of an archdevil or devil lord?

I would treat it the same as Globe of Invulnerability, so that even upcast spells don't work. Counterspell is a 3rd level spell even if it is cast at 7th level, the spell itself is 3rd level 

Based upon the reading of their lore, it seems that they are more solitary, looking for power and influence for themselves. They've sought to get our of the nine-hells and the ritual that made them is d; almost implying that they are not part of the normal hierarchy and promotions as others 

But as a DM, you can as you will

A Raskshasa's challenge also comes from how they fight. Like you mentioned, they are extremely intelligent and cunning. They usually try to draw their victims into traps to weaken them before hand. They have a solid means of evading everyone by flying, and if they get in a tough situation, they can always just Plane Shift away. Counterspell, you say? Not unless the party is planning on casting it at 7th level. 

Any party lower than Level 13 can't cast a spell that will effect the Rakshasa, which means your magic users are essentially useless unless the Rakshasa knows that one of them can cast deadly spells, in which case they are definitely gonna try to dominate them.

If you play a Rakshasa correctly, the party might not even ever see them. They'll just hear an ominous voice following them as they fall into trap after trap. I would even argue that the Rakshasa wouldn't put themselves within reach of the possibility of a physical fight until they are sure that their opponents are fairly weakened.

6th level or lower. Anything below 7th is useless. The Rakshasa could choose to be affected by it, but I don't see why they would unless it played into their scheme somehow.

good polymorph choice if you want to sneak around, you can't be detected by any spell of 6th and lower. Just cast invisibility and your good to go.

Quote from ItsTheJAM >>

6th level or lower. Anything below 7th is useless. The Rakshasa could choose to be affected by it, but I don't see why they would unless it played into their scheme somehow.

 It is still useful though, for example they might need healing from a servant.

Fellow Critter!

You could just cast True Seeing with a 7th level spell slot.

Or let themselves by polymorphed and captured, only to be brought to their base and lead its servants to the PCs. Actually, I should use that...

I'm considering using a rakshasa as a manipulative NPC for the party, but I'm left wondering if a Paladin's Divine Sense will be blocked by the limited Magical immunity? It's a 1st level character ability and not a spell but if it's not blocked, the Paladin in the party is clever enough to pop it around the rakshasa the ruse is undone. I guess I have the same question for a paladin's divine smite. It may burn spell slots, but it's not explicitly a spell.

Lol! Nice one!

Question on classification: I know the Rakshasa is a fiend, but would Hold Person work on one? If it could potentially hold a zombie or skeleton of average humanoid size, would the Rakshasa be humanoid ENOUGH for it to work? Let's say for the sake of argument it was cast at a high enough level to actually take effect? I debated with my DM and they allowed it allowing us to win, but I want to be fair and accurate with uses in the future. Thanks for any input!

Quote from SirDrWizard >>

Question on classification: I know the Rakshasa is a fiend, but would Hold Person work on one? If it could potentially hold a zombie or skeleton of average humanoid size, would the Rakshasa be humanoid ENOUGH for it to work? Let's say for the sake of argument it was cast at a high enough level to actually take effect? I debated with my DM and they allowed it allowing us to win, but I want to be fair and accurate with uses in the future. Thanks for any input!

 Hold person would not work (nor would it work on humanoid-sized undead). There's a separate spell for non-humanoids, which is hold monster. It targets any creature rather than only humanoid creatures. Allowing hold person in that situation to work would essentially give it the effects of a spell three levels higher.

Quote from Hearst >>

I'm considering using a rakshasa as a manipulative NPC for the party, but I'm left wondering if a Paladin's Divine Sense will be blocked by the limited Magical immunity? It's a 1st level character ability and not a spell but if it's not blocked, the Paladin in the party is clever enough to pop it around the rakshasa the ruse is undone. I guess I have the same question for a paladin's divine smite. It may burn spell slots, but it's not explicitly a spell.

 Divine sense would still work. Limited magical immunity gives immunity to spells of 6th level or lower, and advantage on saves against higher-level spells and other magical effects. Because divine sense is not a spell and doesn't have a save to be resisted, the rakshasa gains no benefit against it.

Quote from temery2383 >>

Quote from Hearst >>

I'm considering using a rakshasa as a manipulative NPC for the party, but I'm left wondering if a Paladin's Divine Sense will be blocked by the limited Magical immunity? It's a 1st level character ability and not a spell but if it's not blocked, the Paladin in the party is clever enough to pop it around the rakshasa the ruse is undone. I guess I have the same question for a paladin's divine smite. It may burn spell slots, but it's not explicitly a spell.

 Divine sense would still work. Limited magical immunity gives immunity to spells of 6th level or lower, and advantage on saves against higher-level spells and other magical effects. Because divine sense is not a spell and doesn't have a save to be resisted, the rakshasa gains no benefit against it.

 Perhaps you could use a Doppleganger (with levels of Spellcasting, if you want to inflate it’s CR) secretly serving something like a Fiend?

A Shapechanged Monstrosity is less likely to provoke detection abilities.

That really helps me understand the thinking that a rakshasa would be doing, but plane shift is only on willing creatures?