Divinity: Original Sin 2 has one mechanic that governs everything else, and half the players who bounce off it never had it explained. Every character carries two separate armour bars. Physical Armour blocks physical damage and, crucially, blocks every physical crowd control effect. Magic Armour does the same for magic.
Knockdown, stun, freeze, charm, none of them land while the matching armour bar is above zero. Not reduced odds. Zero chance.
That single rule decides your entire party.
Why mixed parties fall apart
If two characters attack physically and two attack magically, you spend every fight chipping both armour bars on the same enemy and stripping neither. Nobody gets to land crowd control, and crowd control is how fights are won in this game.
Commit the whole party to one damage type. Four physical characters strip Physical Armour four times as fast, and then knock the enemy down and kill it while it lies there. Four magic characters do the same through Magic Armour.
Mono-physical is the more forgiving of the two. Magic parties hit harder late but suffer through the early acts, where Magic Armour is often higher than Physical.
This is not a preference. It is the difference between the game being hard and the game being unfair.
Warfare is the universal physical stat
Warfare boosts all physical damage. All of it. That includes Necromancer spells, which is why the strongest Necromancer builds put more points into Warfare than into Necromancer.
The pattern repeats across the tree. The ability that boosts a damage type outperforms the ability that unlocks more spells, because you will only ever cast three or four spells per turn anyway.
Take a school to the level that unlocks the spells you actually want, then dump everything into the damage multiplier.
Attributes, briefly
Strength, Finesse and Intelligence are your damage stats and you pick exactly one. Constitution is health and the vitality requirement on shields.
Memory buys spell slots and nothing else. Take the minimum you can live with.
Wits is the interesting one. It gives critical chance and initiative, and initiative decides whether your party acts before the enemy does. Going first in Divinity often means the fight is over before the enemy's turn, so a few points of Wits buy more than their raw numbers suggest.
Source points and the spells that end encounters
Source points are the limited resource behind your strongest abilities. You start with one, gain more through the story, and refill at Source fountains or by draining corpses if you are that sort of person.
The Source spells are genuinely different in scale from everything else. Apotheosis resets your ability cooldowns. Skin Graft resets your armour and, combined with Apotheosis, produces the single most broken turn in the game. Players who discover that combination usually stop playing on the difficulty they started on.
Surfaces are damage, cover, and a trap
Fire, water, poison, oil, blood, electricity. They spread, combine, and persist through the whole fight.
Water plus electricity stuns anything standing in it whose Magic Armour is gone. Oil plus fire creates a burning field that keeps dealing damage. Blood conducts electricity exactly like water does, which matters because there is blood everywhere by turn three.
The trap is your own surfaces. A Pyrokinetic who ignites the floor has also blocked the path their melee ally needed. Surface control is a party-level skill, not a character-level one.
Elemental Affinity is the talent that makes surface builds work: standing in your own element cuts spell cost by one AP, which over a full fight is an extra spell every other turn.
Talents worth building around
Lone Wolf doubles your attribute and ability points and raises your armour and vitality, in exchange for playing with two characters instead of four. Two Lone Wolves are stronger than four normal characters by a wide margin. If you want the game to be easy, this is the button.
Glass Cannon grants full AP every turn and removes your armour protection against crowd control. Spectacular and suicidal.
The Pawn gives a free movement each turn. It sounds small and it is one of the best talents in the game.
Executioner grants AP on a kill, which turns a good turn into a great one.
Origins change more than dialogue
Fane, Lohse, Ifan, Sebille, Beast and the Red Prince each carry unique tags that open conversations and quest routes a custom character never sees. Fane in particular reshapes several encounters because undead physiology inverts healing and poison.
Playing an origin character costs you nothing mechanically and gives you a genuinely different script. A custom character is the weaker choice unless you specifically want a blank slate.
The Divinity: Original Sin 2 walkthrough covers act order and the fights worth preparing for.
