This month is terrain month! But before we get too deep into the intricacies and details I think this topic could use a little overview. If you’re anything like me, terrain often times winds up slipping your mind, and gets overlooked. Terrain comes in a lot of different forms and you can probably think of a few during these winter months. So let’s take a look at terrain types.
Ground: Firstly and most obviously we have literal terrain, the ground you walk on. Difficult terrain of the most basic sort reduces movement rate by half by making each 5 ft square require 10 ft of movement to get through. This can be anything from rough uneven ground, to tall tangled grass or vines, furniture like tables and chairs, low walls and the like, or of course snow or slush. These are the most common example but there’s a plethora of other options. One step above regular difficult terrain; there are some types of terrain that are incredibly uneven rough or difficult to pass which require 20 ft of movement for a single 5 ft square. On top of the movement penalties it's impossible to run or charge through difficult terrain, nor can you take a 5 ft step. And of course above that is impassable terrain. Things you cannot normally move through at all such as stone walls and solid earth. And of course these things can affect your overland movement going from one place to another in exactly the same ways.
Squeezing: If you are moving through a space you can fit through, but smaller than your space you have the misfortune to be squeezing. This causes you to move slower like difficult terrain but also imposes -4 to attacks and ac. Technically this doesn't restrict the weapons you can use, but your GM is well within their rights to decide your greatsword is useless in such a space, or that your dagger takes no penalty.
Higher ground: If you have more elevation than your target, but can still reach them you gain a +1 bonus to your attack. Super simple stuff.
Cover: The basics of cover are pretty simple. If an enemy has to shoot or swing around an object that grants cover to hit you, you get a +4 bonus to ac. specifically if you can draw a line between the corner of a foes square, and the corner of you square, which passes through cover, you get the bonus. You also have to be within 30 ft of the cover and you have to be as close as or closer to the cover than the opponent is. On top of that you also gain +2 to reflex saves if the origin of the effect is opposite to the cover. And of course with cover one can make a stealth check to conceal themselves from sight. And it’s not just objects that can provide cover, creatures provide the bonus to ac, though not to reflex saves, just like an object which makes hiding behind friends and foes an invaluable tactic. A large or larger creature picks any 5 ft square to calculate cover from giving them better chance to swing around such barriers, but those attacking them can pick any square they can reach to calculate cover against, it cuts both ways.
Cover has a few variations depending on the situation. Partial cover confers only half the ac and reflex bonuses, while total cover doubles them instead as well as granting improved evasion and a whopping +10 to stealth. The best cover though is total cover. If there are no corners from the foe’s square that lead to yours without passing cover than they can’t attack you whatsoever, and likewise an area of effect ability is only going to harm you if it blows through your cover first. Speaking of destroying cover, it is not implicitly stated that the cover takes any damage from this process. What I would recommend is that an attack which misses the target due to cover should deal damage to the cover instead. What does and doesn’t grant cover and in what amount is ultimately up to the GM but generally it’s pretty easy to interpret.
Concealment: Similar to cover, if a line connects your corner and a foes and passes through something granting concealment you also gain a significant defensive advantage. This generally comes as a 20% miss chance on all attacks directed against you. If the concealment is thick enough it can grant a 50% miss chance. Just like cover, concealment allows you to hide and can also apply penalties to movement depending on the source of concealment. Concealment can be caused by anything that obstructs sight, but not physical attacks such as fog, smoke, darkness, weak vines, paper screens and more.
Hopefully this has been helpful both in letting you better understand these tactical mechanics, and in framing and understanding some of the articles to follow this month.