A pointless, overly complicated overhaul of the DnD Combat system


Movement
========

Current DnD movement speeds become the maximum, and the default half of that.
For each square (or hex) you move beyond the default, you pick up one Momentum.
On your next turn, you must move at least one hex for each momentum you have.
This represents that covering such a large distance in a short period of time
doesn't give time for you to slow down.

If you are taking the dash action, or your movement speed is otherwise increased,
momentum only kicks in when you exceed have of the modified movement speed.

Momentum also affects your armour class.

Defence (Armour Class)
======================

This is now broken down into two sections:

 - Evasion
 - Blocking

When an attack is rolled, if it is compared to the defenders evasion.
If the attack roll is below the evasion score, the attack 'missed'.

If the attack does not miss, the attack roll is compared to Evasion + Block.
If the attack roll is less than the sum of evasion and block, the attack is 'blocked'.
Only stagger damage is applied.

If an attack does not miss, and is not blocked, then regular HP damage occurs.
(Optional rule: the difference between the attack role and total AC is the max HP damage that can be taken)

Evasion
=======

Evasion is:

 -  5   Base
 - ±2   Size class (smaller is positive)
 - +a   Your acrobatics modifier
 - +a   Your athletics modifier
 - +m   Your current momentum

Blocking
========

Blocking comes primarily from armour, shields, and parrying with weapons.
Shield and parry bonuses only apply if the attack is coming from a reasonable direction for them to do so.
Otherwise, the AC stats for these are not modified from DnD 5e (armour is assumed to be a modifier above 10)

Stagger Damage
==============

Stagger Damage represents how steady on their feet a character is.
Most combatants have stagger points equal to:

 - 20  Base
 - +p  Profiency Modifier
 - +s  Strength Modifier
 - +c  Constitution Modifier

At the start of each round, you regain stagger points equal to your dexterity bonus.
You can also forfeit any of the main three sub-actions (move, action, bonus action) to regain 5 stagger points.

If you run out of stagger points, you are laid out prone (standard dnd 5e rules for that).

Attack Rolls
============

Same as 5e, except you add half the target's current stagger damage to the roll (or remove it from AC).

Damage
======

Damage is rolled so long as an attack doesn't 'miss' (even if it is 'blocked').

This is where I'd like to do another massive overhaul, but this is already complex enough
Ideally, weapon damage would be a lot less random -- but that's a lot of balance work.

Instead, a few notes about damage types:

 - Piercing and magical damage does not deal stagger damage. If piercing damage is 'blocked', nothing happens.
 - Bludgeoning is limited to just base damage for health (no modifiers, profiency, etc.)
 - Slashing deals is divided into stagger and health, with stagger being up to the defender's blocking stat. If the slashing damage does not exceed the stagger, no health damage is dealt

Random Changes
==============

Sneak attack does not get additional damage die, but instead additional to-hit dice.
(Or, you could house rule it as not being able to be blocked)

Unarmoured Combat...eh, make it up. Double the modifiers, but you get no block

Example
=======

A human fighter charges into combat.

Their stats:
 Str 16 (+3), Dex 12 (+1), Con 15 (+2).

Their Base AC:
 Evasion: 5 + 5 + 1 (base, athletics with profiency, acrobatics without)
 Blocking: 6 (Chainmail), 2 (Shield)

So, 11+ hits, 19+ deals damage (17+ if they you have them flanked so they can't use the shield)

If they run into combat using all 30ft of movement, they will have 3 momentum bonus, changing the AC to 14 to hit, 21 to damage.
This means that unstaggered, a sprinting fighter is very hard to damage -- however, any attack over that 14 will start slowing them down, and every two points of stagger damage brings down that target AC.