Alright, here we go;
-The naga is basically impossible to ambush, as
Detect Thoughts lets it detect anything sentient that gets within 60 feet of it (works through up to 3ft of wood, which is most trees); particularly thick jungle foliage
could reduce that range dramatically, but would prevent people from lining up a shot with a ranged weapon similarly (also, it can see perfectly fine in complete darkness)
-Natural armor comparable to giant's hide or (young) dragon scales, before it's
armor buff (while still having superior reflexes for it's size).
-21 strength (18-19 is typically the absolute peak for humans), before it's
strength buff (which gives it giant strength)
-Poison spit from up to 30 feet; it's not
quite a guaranteed or instant kill (one minute between initial and secondary damage), but unless you have a superhuman constitution (or are really lucky), you can expect to kiss half or more of your health (and associated bonuses) goodbye (until it poisons you again by spit or bite)
And then there's the really fun part- it's spells.
Ambushing? Once you've detected your
opponent victim, use
Greater Invisibility to sneak in, followed (optionally, depending on the opponent's hearing/alertness/reflexes) by
Expeditious Retreat and
Divine Favor to catch the opponent before it can react, constrict and apply Divine Power, poison bite until the opponent submits.
Forced into ranged combat (somehow)? Good thing you put up your Mage Armor up to nine hours ago and have an
arsenal of attack spells!Melee combat? See above- it's hard to wrestle something that's up to 20 feet long and up to 500 pounds (did I mention it's as tough as giant, too?)!
Actually
losing a fight? Stick a Light spell on the closest thing to his face, then Greater Invisibility and Expeditious Retreat out of there so
you can heal. Is he still following you on your Detect Thoughts?
Lesser Restoration your fatigue away and prepare another ambush! If not, slink away and rest to restore all of your spells.
Oh, I almost forgot- you will of course remember to slap
Dispel Magic on all of your opponents who have magic items or spellcasting ability (with the sole exception of Sauron's ring).
Any questions?