You will have to test it to check on my thoughts but Reggie needs either speed or slows to stay alive. You didn't opt for high health in that build and you have no speed items. Therefore anyone who attacks you will be on you like white on rice and you cant take a beating for long. Your only defence against this is the mines and in my experiance mines are not enought to stop a player who's got my number.  Also you have tons of mana but can't possibly use it when under attack as snipe is useless in close combat and mines have a fairly long re charge. The build might work as a shy regie, but I mean very shy.

   If you find what I say to be true when you play it try putting in tracking device, it is awesome with snipe. Drop a bit of the mana (keep serpent blade though) and add some health or Wyrmskin gloves to improve your ability to bail on a fight gone bad. Consider getting at least one rank of MotB, not for the damage but for the slow ( trust me when somone is trying to kill you they will use their abilitys so it will go off). Let us know if any of this makes it go beter or if your strat works beter as is.

tradjik, as per IllegalDustbin, having the ability to refill my mana bar every 45s is more useful if you have a larger mana pool. 

Grotto, often times I'll throw in a Tracking device into my build, just so snipes are more powerful. But as this is currently a snipe-light build, I usually omit it. Also, if you didn't see it, my build does use Mark.  It's just called "Mark" not "MotB". And yes, I do tend to use this build more for hit-and-run type tactics.  Lay some mines, engage, pull enemy onto mines,mark, more mines, and hopefully by then they're scared/ready to die. 

Your progression is very weird.  Mine 3 is such a huge upgrade that I can't imagine this build getting the pretty mediocre AF 2 instead of it at level 7.  Similarly you get AF 3 at level 9, and so do not get mark rank 2 until level 11.  Mark 2 is awesome sauce, especially with shrapnel mines, whereas AF gives.... +25 damage.

Lastly I agree that both Vlemish and Plenor is too much. Yeah mana is nice, but you should be either a bit more careful in your ability useage, or use the BotS a bit better, Grab unbreakable boots for mana instead of the Plenor battlecrown.  Half the mana, but you get some much needed HP too.

I had been assuming you got both, getting just one is pretty reasonable.  Though I admit that I often opt for just the Boots though, but I also go with Blood of the fallen, and eventually land a heart of life. So these are pretty different builds in general.