Combat

Initiative, rounds, surprise rounds
In the general case, we have two sides facing off: our party, and the enemy. Each side is aware of the opponent, and proceeds to enter combat. Characters take turns attempting to hurt the opponent. The order in which characters take action is determined by Initiative. At the start of every combat encounter, you calculate your initiative by rolling a d20 and adding your DEX modifier (and any other applicable modifiers you have). The DM will be rolling initiative for each opponent. The character (player-controlled or NPC) with the highest result goest first, and then down the list until everyone has had their turn, then back to the fiirst one.

One complete cycle through the list of combatants with everyone taking their chosen action during their turn, is called a round.

Every now and then, the situation may be a little different. An enemy may jump on the party from behind some cover, catching them unawares, or out a secret door without anyone expecting it, while everyone has their back turned, etc. In such cases it's not realistic to assume, like above, that "each side is aware of the opponent" before starting to take turns based on initiative - it makes sense that the attacker will manage to land some hits before the defender realizes what is happening. This is known as a surprise round, and basically means that any combatants aware of the opponent have an extra round before everyone else (only they will roll initiative and act during that time, while the rest are figuring out what is happening). A character who is attacked while surprised (someone hit you before you realize it), losed their DEX bonus to AC (this is known as being flat-footed). Once the surprise round attack is over, everyone else can now also roll initiative, and a normal combat round follows.

The combat grid and movement
During combat, the ground is represented by a grid where each square = 5"x5" space. You will be choosing your positions on the grid at the start of combat, of course taking into account where you were just before that.

During your turn, you can move across any distance allowed by your base speed. (move action - see below). If you choose to not take a standard action during your turn, you can take a second move action, and cover twice as much distance if you wish.

Types of actions in combat
Things you can do in combat are either free, standard, move (or move-equivalent) or full-round actions.

Most combat actions are standard actions (can be performed in the space of one turn, with probably a second to spare) - attack with a weapon, cast a spell*, use a magic item, drink a potion, etc.

* Some spells require a full-round action to cast. This will be included in the spell description (for example, "casting time: 1 round")

A move action represents the time you take to move across the grid. Or, you can do something else that takes approximately equal time or effort. Such actions are: draw a weapon, pick up something from the ground, stand up from a sitting position, sheathe a weapon, etc.

Free actions are considered taking up very little or no time/effort at all, and can be used at any time. For example, dropping something, or calling for help.

A full-round action is used when you do something that's consuming all your effort during your turn. This is usually the case when you have an ability or feat allowing you to make more than one attack during your turn (but doing so takes the full round). The only movement you can make with a full-round action is a 5-foot step (to the next square). In most cases, however, you can still use free actions with your full-round action, unless the DM objects for some reason.

When it's your turn, you can either:
 * use a standard action + a move action, in any order (or only one of those). For example: move across 4 squares and attack. (you must have your weapon out)


 * use two move actions - еxample: Draw your weapon and move to the enemy (but you can't attack during this round)

You can choose to go into "full defense" as a full-round action. During your turn, you get -4 attack, but gain +2 AC. If you decide to hold your action, you move to the top of the initiative list for the next round (only the next round). For any rounds after that you're back at your original initiative. Aiding another is treated as a standard action, so you can accompany it with a move action if you want.
 * use a full-round action - examples: Make two or more consecutive weapon attacks (if you have an ability that allows it); or: Cast a spell with 1-round casting time
 * take no action
 * aid another - instead of yourself attacking the enemy, you help someone with their melee attack. You must be in a position to make a melee attack. Make an attack roll against AC 10 - if you succeed, your ally gets either +2 attack, or +2 AC on their next applicable roll (you decide which).

The 5-foot step
The 5-foot step is a special kind of semi-free action. It's what the name says - a 5-foot step, that is, moving from one square to the next. You can use it together with any action in a turn, even with a full-round action; but you cannot use it together with any other movement during the turn (only actual movement counts - move-equivalent actions are ok). A 5-foot step does not provoke an Attack of opportunity (see below).

Threat and Attacks of Opportunity
The concept of threatened area is this: every combatant threatens all squares that he or she can attack with a melee weapon. That's usually all squares adjacent to the one he/she is in, or even further if the combatant is using a reach weapon.

When you move out of a threatened square (other than with a 5-foot step), the enemy threatening it can make an immediate attack against you, outside of their regular turn. This is called an Attack of opportunity.

You also provoke an Attack of opportunity if you cast, or start casting a spell, while you are in a threatened square. (Unless the enemy doesn't realize you're casting, for example when your spell has no visible or audible components.) Normal weapon attacks against the threatening combatant do not provoke an attack of opportunity. However, if you're standing in an enemy's threatened area, and attack another enemy (whether in melee or at range), the enemy currently threatening the area will have an Attack of opportunity against you.

Attack rolls and damage
Okay, so finally you get to swing a weapon at the adversary. Make a d20 roll and add your base attack bonus plus any other relevant modifiers if you have any. The aim is to get a result at least equal (or higher) to the enemy's AC. You're not supposed to be aware of what exactly his AC is, so the DM will tell you if you managed to hit the enemy or not.

If your attack didn't manage to beat his AC, your strike misses.

If you did hit, roll the relevant dice to determine damage. Every weapon has its own type and number of damage dice. Your damage roll is deducted from the enemy's hit points.

If you rolled 20 with your attack roll, you hit regardless of the opponent's AC. In addition, your strike was remarkably effective and you have a chance to deal more damage than usual. Repeat the roll. If you manage to hit (just beat the AC, you don't need to roll 20 again), you land a critical strike, and your weapon damage is doubled.

All this works absolutely the same way when an enemy makes an attack against you.

When one of the combatants runs out of hit points, he or she is out of the reckoning. (At 0, you're dying. You may be saved yet, but you cannot continue fighting. At negative HP, you're dead.)

Combat spellcasting
The things to remember:
 * You provoke an Attack of opportunity when you cast or start casting a spell. If your casting time is more than one round, you only provoke an Attack of opportunity when you start casting, not during the subsequent rounds (but if you're attacked during those, you still need to remain concentrated - see below).


 * In order to cast successfully, you need to be focused. If you start casting and someone attacks you, there's a chance they'll hit you and break your concentration. In this situation, you need to make a Concentration check (DC 10+damage taken+spell level). If you succeed, your concentration is unbroken and you proceed with your spell. If you fail, you can't finish your cast, and you also lose that spell from the list of prepared spells or spells per day.