Advanced rules: rerolls and levelling

So, now that we have the essentials covered, let's move on to some of the more advanced rules in the game.
First of all, I have introduced a "hardmode" that the campaign may use, should the players and the GM so desire.
The hardmode is simple. Every time you roll a 6 on one of your dice, excluding the damage rolls, you re-roll that die and add the total value (the 6 you first rolled + the new value) to your overall roll.
To example, I roll 4d6, and ger 1, 3, 5, 6. Without hardmode, that roll would be accumulated to a total of 15. With hardmode, on the other hand, I reroll the 6, and let's say I get a 2 as the second result. That gives me a total rolled of 17, instead of 15.
This is done every time you roll a 6, not counting damage dice.

Leveling
Well then, we can fight and do stuff, so let's go on with detailing character progression. Levelling is rather simple. Every time your GM decides that you have done enough to level, be it through accumulating experience points or story progression, you level up. Upon leveling up, you gain health and mana depending on your end and will attrubutes.
You gain 1 + 1/2 of your end exceeding 10 as health.
So if you have 14 end, you gain a total of 3 health per level.
You gain 1/2 of your will exceeding 10 as mana.
To example if you have 14 will you gain 2 mana per level.