How to kill it?

It has 4000hp and recover 250hp/ 3sec

I can only manage to damage it to 3000 hp
I have a spear with 89 damage and a toxic sword from mission
I am level 16 with 1500 gold

What is your class and skill set? One of the key things about this boss is to either avoid his poison cloud or interupt it through a skill or by stunning. I found stunning him to be the most effective method, but this is one fight where you need to time things well.

Get the poison weapon by getting a poison sample from the pot of the first boss and showing it to the guy beside the scarecrow.(forgot which one). ITS KEY to killing him IMO. poison just destroys him slowly. spam attacks. Just get moves that cancel his poison cloud before cast.

I went at him with blade storm, slam and doom blade. Just keep hitting, running, and it'll finish him.

The key is to avoid the poison cloud and keep striking him. I was level 15 when I defeated him.

how do u beat him with the assassin class

I beat him on hard with Assasin... and man was this fight hard! ;)

* Fighting on hard is... well very hard. It's not going to be a piece of cake but tears & sweat, and a bit of luck maybe. At least that's how it was for me.

*Level 15?
I really hope You re-speced and grabbed that sweet ultimate skill.

* Most bosses forces You to think about tactic. Some forced me to to some re-spec as well. I really like it about this game.

* Assasin vs Takeshi
This boss will really test You! It's mostly about maxing Your DPS while keeping up with the heat. You'll need best gear, skills and small room for mistakes.

Not much to say if I remember correctly I was using build my standard build with Shadow Reflex + Shuriken (maxed), 1 point in Spectral Dash (mostly for avoiding) and Shadow as ultimate skill. Spare points went for healing skill (try to cast when they are busy with Shadow / when using Vanish).

And don't forget about good old "kick, strike" combo - even if You didn't invest any skills contributing.

Any tips for Warrior Class?  None of my attacks seem to stop him from doing his poison cloud thing, and if I run away from the cloud he totally heals himself before I can get back to him.

Aha!

The secret to defeating Takeshi as a Preist is to Summon Shadow and while Takeshi is distracted, use Shadow Bolts. Make sure to stay out of the poison clouds.

It may take a little longer than other bosses but it's effective.

I'm having a great deal of trouble with him on Warrior on hard mode, I have to admit. i'm only level 14, so I can't get an ultimate skill yet, and he just heals for too much! I should probably Re-Spec, but I don't know what to get!

Here's some small tips based on my gameplay, but if your class is priest, sorry i cant' help you there just yet.

Warrior
At this rate you have the great advantage of damage and deadly techniques like the multiple strikes and Doom blade, And more importantly you must maximize the stats of Iron hide and cure to aid yourself in combat. The important part is that you have to be swift and think fast if he cast the poison cloud, Just wait for him to get out of the poison cloud and that is your opportunity to strike at will, but don't crouch to defend yourself in the cloud, you will still be left vulnerable due to stun effect and increases 25% more damage.

As for the assasin's class im still currently playing it of how this works, but i gotta tell you, it kinda sucks on giving damage and makes my gameplay more hard.