How do I kill it

It instantly kills me. I have Full soldier armor.

 

That's T2 armor. You on a Beta world? If you're higher than beta, I'd go back and farm for gear.

Or is that a legendary? Red particles coming off him? Hard to tell. They're sometimes very tough, avoid him or, worst come to worst, go to a different world, that monster wont be there.

 

If something one-shots you. Its likely a good idea to give it a pass...
http://images.wikia.com/dragonball/images/5/55/Kid_Gohan_Running_Away.gif

 

it's a random mini-boss monster. Right now they're badly over-tuned and basiclly one shot you unless you're wayyy over gearred. Best bet is to try set up a platform to shoot at him from safely if you stubbornly refuset to run, hide or avoid it

 

That's a legendary. I can see the red particles coming off of him.

Yeah. The damage from land legendaries is insane. You're better off avoiding them or cheesing them right now.

 

Mini-boss monsters (for me atleast) require me to be in the best armor of that tier and to keep healing stuff handy. (also make sure to try and dodge alot, since even in the best armor it seems like most of them still 2 shot me)

 

Sky bridge it

 

build yourself a little bunker with an opening and shoot it with a gun or a bow

 

Well i killed (cheesed it)

is what it dropped

 

But seriously, I know what that's like. But sometimes they drop good stuff, I got my first (and current) gun from one on a Gamma planet.