How to make a low CR villain more dangerous

My PC’s in one campaign are currently traveling to their first major town and, unbeknownst to them, there is a Rakshasa, disguised as the town mayor, using the town to feed and kill as he pleases while performing experiments on the town’s populace etc etc other evil acts. While I like the character I have made for him so far, and don’t want to give HIM more powers, I need him to be more of a threat in the story.

Rakshasas focus mainly on deception and trickery, But aside from literally turning the PC’s on each other (which I’ve thought about) I can’t think of alot of ways to add more depth to this villain. The town has a Thieves Guild indebted to him, and he has several Chuul under his command, working for an Aboleth that is his master, but this would still be a pathetic fight if I just threw them at the PC’s.

The CR of a Rakshasa in 5e is 13, the party is comprised of four characters at level 6. This seems rather even, but Rakshasas are very non-combat focused, so the CR is only a rough estimate of his abilities

The goal for this villain is to be a Master strategist. The Rakshasa is arrogant, so he’s likely to reveal himself too early to the PC’s depending on how things work out, and I’m okay with that, but he should not be caught flat-footed. What are some ways I could use cleverness or manipulation to give him the advantage in an urban setting against PC’s that like to get violent?

The best way to do this would be with the least amount of flair. The Rakshasa needs to keep his cover or lose all power in the town, so blockading and attacking the PC’s needs to require the least amount of overt effort on the part of the Rakshasa. Subtlety is key.