So, I've been watching a bunch of old shows on Netflix recently, and there was an episode about something with a very similar name - The Rakshasa. I think they were probably the same thing, especially since it's been a while since I read my Monster Manual, and might be misremembering the spelling (Something there's even more evidence for, since a commenter used "Rakshasas" elsewhere)
Why wasn't it the creature in the Monster Manual? Now, I know I just said that they're the same thing. But really, they aren't. You see, the Rakshasa reads your mind to see who you trust, turns into them, and then, if you don't kill it, tears you apart. Instead we have a humanoid tiger that can use magic. Why not just use the mythical creature when it's so much cooler?