What is an attack of opportunity?
An attack of opportunity, or "opportunity attack," basically represents a situation where your enemy drops their guard long enough for you to slip an additional attack in. It is most commonly provoked in the following ways:
- Moving out of a square adjacent to an enemy. Let's say that you're beside a monster, and you want to move to fight another monster. If you don't shift (and just walk or run) and you move out of that square, that monster gets to attack you; think of it like turning your back on the enemy to move away.
- Using a ranged attack while adjacent to an enemy. This would be where, for instance, you're attempting to fire a crossbow while an enemy is next to you. That enemy is not going to wait for you to load the crossbow with a bolt, aim, and fire - it's going to take that moment of vulnerability and strike.
Opportunity attacks always interrupt the action that triggered them (moving or using a ranged attack), such that the action is resolved after you make the opportunity attack. You can read a better explanation on pg. 290 of the PHB.
Is blast just a cone? Does it hit 1 square in front of you, 3 squares behind that square, and then 5 squares after that?
A blast can be a cone in terms of flavour, but mechanically, it's a square. Blast refers to an attack that affects an area adjacent to you, and the number identifies the length of each side - so, a
blast 3 attack creates a 3x3 square. You can generally pick where the origin square is (where you start "drawing" those lines) but it has to be adjacent to you, in most cases. This is typically clarified by calling it a "close" burst (where close refers to essentially centering upon the attacker). Additionally, there must be a line of effect from the origin square to the target; for instance, you cannot go through a wall even if the square is large enough to encompass it.
A similar concept, but it is less frequently centered on an adjacent square and is more commonly ranged (using these also provokes opportunity attacks, generally). Instead of the number defining the length of each side, the number refers to how many squares it radiates outward from the origin square; so, for a
burst 2 the attack extends 2 squares in any direction from the origin, ultimately creating a 5x5 area (the same as a
blast 5). They may also be close, in which case it's assumed to radiate outwards from you, the caster, rather than a target origin square.
How does charge/bullrush work?
A charge lets you move your speed as a standard action, but you must move closer to the enemy, and you must move at least 2 squares from where you start. At the end of the charge, you may make a basic melee attack or a bull rush. You get a +1 to the attack roll for whatever you do. You can take this after a move action, such that with a speed of 6 you could move a max of 12 spaces with a charge.
A bull rush is a Strength vs. Fort attack, without weapon modifiers. If you hit, you push the target one square and move into the space it just left. There has to be a space for your target to go into, or you can't do it. By itself, a bull rush does no damage, but there are situations where it might (pushing somebody off a cliff, for example).
What advantages or disadvantages do you gain by being prone?
Advantage:
- +2 to defenses against ranged attacks.
Disadvantages:
- You can only move by crawling, which is half your speed.
- -2 to defenses against melee attacks (combat advantage against you).
- You take a -2 penalty to attack rolls.
How do healing surges work, and are they the same thing as second wind?
Healing surges basically represent your ability to heal. They are typically spent in combat by healing powers (like a Cleric's or Warlord's), healing potions (which spend 1 to regain 10 HP, rather than the actual healing surge value) or, indeed, a Second Wind. Once per encounter you may use your Second Wind to regain one surge's worth of HP and gain +2 to all defenses until the start of your next turn. You can also spend as many healing surges as you like during a short rest, where you trade
x number of healing surges for the healing surge value, up to your maximum HP.
Hope that helps.