I noticed that every spellcaster class have an entry called Magic Damage Die, or MDD. Sorcerers have a stated MDD of "d10", wizards a "d6", and so on.
How exactly those numbers affect something in the game?
The Magic Damage Die, or MDD, is what you actually rolls when casting a spell that does some form of damage.
Spells on DWRPG have a really distinct feature: they don't have a fixed die of damage, as it was on Pathfinder and D&D. When you look at a spell description, you will see something like this:
Notice the "1d per caster level". That means that a Fireball spell, cast by a 10th level wizard, would deal 10 dice worth of fire damage.
But which dice?
That's where the MDD comes in. Each class have a certain die as its MDD. Wizards have a d6 for its MDD, so when the wizard from the example casts a Fireball, it would deal 10d6 worth of fire damage.
Some classes have different MDD's. Sorcerer, for example, have the biggest "natural" MDD of the game, d10, feats and builds aside. That means that, when a 10th level sorcerer casts the same Fireball, it would deal a whooping 10d10 of fire damage, almost the double of what our wizard could put up.
This is meant as a balancing mechanic. Wizards have a gigantic repertorie. Sorcerers have an awesome damage output. Clerics and Druids fall somewhere between, having a good, meaty d8 as their damage die - but having far less impressive, flashy spells. Each class will have a MDD that balances the other features of that class - spontaneous vs prepared spellcasting, daily limit, spell list, etc.
Some feats and specific builds can raise the MDD for a given spell. So, let's say that our sorcerer is a 10th level sorcerer from the Fire Elemental Bloodline. He will have this Bloodline power avaliable to him:
If there's not any other effect that changes his MDD, this sorcerer would be casting a massive Fireball capable of doing 10d12 of damage! That's a TON of damage, and where the Sorcerer show his shine most.
A Magic Dampening spell, on the other hand, lowers the target MDD one step down for a while. So, a regular Sorcerer hit by this spell would deal damage using d8's, instead of d10's (before considering other effects).
Disclaimer: I'm the author of this system.