Minmaxing in D&D Next

I have a player at my table who is playing a death cleric. He is using a scythe as a polearm which we have agreed is doing a d10. He has some class feature that allows him to do an extra d8 three times a day for the entire combat. When he hits a target he is able to make a second swift attack. Finally, he has some kind of polearm feat that gives him threatening reach.

So while my other players are doing like a d6 per round this guy is often doing 2d10+2d8+2 which just seems completely broken.

My first question is am I missing something--I am fairly new to D&D Next and some of this character optimization may not be legal--can anyone validate that what this player is doing is actually possible RAW?

My second question is, does D&D Next support 'system mastery' in the same was a 3.0? Do 'advanced' players have significantly more powerful PC's simply because of rule mastery? 

I remember in 3.0 building encounters to just shut down certain PC's & prevent them from doing their 'tricks', I did not find I had to do that as much in 4.0 and I am curious if we are returning to those types of encounters?

Here is video of Thor's PC in action

Shannon Error Magic style

Problem
I often have unspent mana during my untap step. Since I started playing UG I am seeing more of this. Some of it may be acceptable because I am holding mana back for counter spells which I do not need to use, but I am concerned that my mana ramp is not aligning with my deck and/or my draws.

Error Definition

The Shannon Error  is based on one of the Great Lewis & Clark explorers, who thought he had fallen behind, when in fact he had gotten ahead, of his team. So he rushed to catch up, which only compounded his problem by moving him further away from the rest of the expedition and further from much needed supplies.

From Shannon's experience, we can deduce the Shannon Error: the pursuit of a goal with great effort, the attainment of which is through less effort, not more; or, trying to catch up when you are already ahead.

Example

My current concern is that I find myself often not spending all of my mana each turn. This happens in two ways--I create I have found that this happens to me a lot in magic. New to the game, I find myself drawn to large Timmy creatures that have clearly defined rolls on the battlefield.

Thus, I am a big fan of any thing that encourages Mana acceleration so that I can get these guys out as soon as possible.

Solution

Actual Play Legacy of the Crystal Shard--D&D Encounters S16 S1

Legacy of the Crystal Shard--D&D Encounters S16 S1

I am DM'ing this Season of D&D Encounters at Mercenary Market in Costa Mesa, CA. 

We are using the D&D Next rules, which I have not read.

My plan it to run a fairly loose and off the cuff campaign.

I started this by modifying the first encounter to involved Plague Touched Arctic Creatures [I plan to use a lot of Spell Plague stuff this season--since it will likely be completely retcon'd by the Sundering, I may as well do my best to make it memorable].

I started with a spell touched arctic hound to replace the Crag Cat in the adventure

And because I had twelve players at my table, I added a Plague Touched Boar.

FEAR IT!

The party slaughtered them no problem--D&D Next threat level is very old school--everything is fairly squishy in ways that are often unpredictable.

Jake is playing a mage. Brian is playing some kind of Hip Hop bard. Scott is playing Drizzt. Thor is playing a broken Death Cleric.

Sarah also has a bard. Jack is a gnome theif.

Will, who actually knows the rules, is playing a barbarian, Cody has a bard or something as well, 

Elizabeth was playing the NPC Aldo--she had not played in a while. Carlos has a knight with a foil riding an ice crocodile or something. Eric is playing Druid the Druid.

The adventure began with the players rolling on my Random Ideals Table:

They made quick work of the Plague Touched Beasts. They split the party to repair Aldo's cart, but I did not know how to take advantage of that--out of practice as a DM, I think. I will make them pay for that next time.

The combat with the Yeti's went well--players learned their characters.

There was not a lot of threat--the Yeti's were very squishy.

Looking foreword to next week.

Unboxing Legacy of the Crystal Shard