TLDR:
Burying your ally is not GOOD, but it can sometimes gain you good things.
The Villain doesn't move about randomly... Only when you fight him and fail to corner-and-defeat him.
You can play the game with a single character. Each character has Skills, Powers (which can be used over and over), and a deck of Boons with which to do their thing. They develop by adding flat pluses to their skills (Skill Feat), updating and potentially adding new powers (Power Feat), adding to the types of boons in their starting deck (Card Feat), or by swapping out the boons in their deck with better ones. Each starting character is "fixed", as are the options to advance (Merisiel can add up to four Skill Feats to her Dexterity, but Kyra can't add more than one). However, there are more options than feats rewarded, so several people may develop the same character different ways. You start with two free characters (Kyra and Merisiel) and can purchase the other 9 with in-game gold or real money.
Each Scenario has a list of locations used. Each location has a fixed deck list. The first thing *I* consider is, "which character will be best to close this location?" Next, I think about who can best acquire the listed boons, and who can handle any "While at this location" conditions best. If you take your whole party to one location at a time, and you encounter the Villain, you can't temporarily close the other locations to corner it. But some characters work best around others (Bards!) so it's all part of the strategy.
Yeah, that was the short version.
Ok, so, one at a time. I may be telling you things you already know, but bear with me.
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Burying your ally... The tutorial mentioned the may ways to "play" a card. Reveal, Display, Recharge, Discard, Bury, and Banish. Those are GENERALLY in order of preference, based on the idea that your Hand and your Deck together represent your current Health. You die when you have to draw a card from your deck and there are no cards left. The most common time for this to happen is when you're resetting your hand up to your hand size at the end of your turn. Having cards in your hand prevents you from having to draw so many cards from your deck. With that in mind:
"Reveal" means to just show that the card is in your hand. It stays in your hand. This means you can use it again at the immediate next opportunity.
"Display" means to move it out of your hand until the card instructions tell you to do something else with it. The "Goodness" of this really depends on this latter development.
"Recharge" means to put it on the bottom of your draw deck. You don't get to play it again any time soon, but it stays in your "health" pool
"Discard" means to put the card in your discard pile. This takes the card OUT of your "health" pool, but many healing abilities return cards from your Discard pile to your hand or deck.
"Bury" means to put the card in that pile of dirt. Only extremely high level abilities can return cards from your Buried pile into play, BUT at the end of the Scenario, the card is availble for rebuilding your deck.
"Banish" means to return the card to the game box. The only way to get it back is to encounter the card again (generally by chance) and acquire it normally.
I believe the tutorial says NOT to be afraid to bury cards for their powers because boldness is rewarded. Personally, I avoid Bury and Banish powers a lot. To answer your question, Burying an ally isn't GOOD, but there are times when it's worth it.
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Villains moving around... And some about locations...
I'm going to make many generalizations about Scenarios. Just be aware that there are exceptions to most (if not all) of them.
A typical scenario card has three main bits of information used to set up the game. There is a list of locations, which tell you which Location cards to set up based on how many characters are playing. Normally, it's two plus the number of characters, so there will be three if there's 1 character, one more for 2, etc. Each location has a "While at this location" condition (special rules that apply to a character who is at that location), a "To Close" condition (the test or action that must be passed/taken to close the location either temporarily or permanently), and "When permanently Closed" text (a triggered action or persistent condtion that exists upon closing the location permanently). It also has a list of (usually) nine cards of the eight types (Monstar, Barrior, Weapon, Armor, Item, Ally, and Blessing) that you mix together to build up that location deck. Then you usually add one more card...
The second and third main bits of information on the cards are which Villain(s) and Henchmen will be used for the scenario. The Villain, usually only one, is static. The Henchmen may include unique "named" henchmen and/or generic ones in a list. Typically, you start a pile with a Villain. Then you add unique henchmen in order until the total number of card in your pile equals the number of Locations. If that doesn't happen, start adding generic henchmen until you have the right number. Then you shuffle and add one card from that pile to each location. Then shuffle the location decks. You play as normal. If you defeat a henchman that is drawn from a location deck, you get a chance to close the location "permanently" by filling that location's "To close" requirement. If you can't, or you try and fail, then you generally have to wait until the location is empty of location cards before you can attempt to close that location. (In fact, if the last card of the location deck is the Henchman, and you defeat it, you get two chances to close!) If you succeed, you trigger that location's "When permanently closed" text.
The Villain is in one random location. It doesn't move about randomly... Only under certain circumstances. When you defeat a monster or Henchman, it's Banished back to the box. If you fail to defeat a monster or Henchman, it's shuffled back into its location. Villains are handled differently. When you encounter (and don't evade) a Villain, the first thing that the game offers you to do is it temporarily close each occupied open location (other than the one where the Villain was found) by fulfilling its "To close" requirement. This "temp close" only lasts until you are finished with the Villain. This can make you think twice if the requirement is something costly.
If you defeat a Villain, the location where you drew the Villain immediately closes (triggering the When permanently closed" text). If there are no other locations that are not closed (either temporarily or permanently), you start a new pile and add blessings from the game box until you have a total number of cards equal to the open locations. (If there's only one, that's just the Villain alone, and the shuffle-animation looks a bit silly.) Shuffle that pile and add one card from it into each open location, then shuffle each of those location decks. (Once that's done, the temporarily closed locations are considered "Open" again.
If you FAIL to defeat the Villain, something similar happens. The location where the Villain was drawn stays open. You gather a pile of the Villain and blessings from the Blessings Deck (thus potentially shortening the game) equal to the number of open locations, and shuffle and distribute the cards in the same way above. Note that it might end up in the same location if you don't defeat it.
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Characters and character development...
You can actually play just one character. In another topic, one of the devs challenges anyone to play Lem solo on the hardest setting through all the released scenarios. Each character is "pregenerated" with skills, powers, and a card list.
Every character has the skills Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma, defined by a die-type. They may have MORE skills based on those first six (Kyra has Wisdom at d12, and Divine listed "Wisdom + 2", so if she has to make a Divine check, she can roll a d12 and add 2). If you don't have a skill on your card, you don't base it on an existing skill at all. You just roll a d4. (If you keep this in mind, it'll explain why dice pools change to d4s when you add bonuses which don't apply to the big six Skills.) You develop these by adding a flat +1 to any roll based one of the big six every time you gain a "Skill Feat" as a Scenario, Adventure, or Adventure Path reward. The choices you have are limited (as you can see on the beige-and-blue bards listed on the Skills tab of your character sheet), but every character has 15 total possibilties, and the entire Adventure Path won't reward you that many, so different folks may take the same characters and develop them differently.
Powers are wide and varied. They include the size of your character's hand and any proficiencies with Weapons or Armor, but then they can get very individualized. This must have been one of the bigger Dev nightmares, coding each and every power. Most characters start with two or three powers on top of their Hand Size and Proficiencies. Every character has four ways to improve their powers through "Power Feat" rewards. (There will come a point in the future where you will choose one of two Roles for your characters, which further specializes them... Each will add 8 more possible power feats. We're still two adventure-releases out from when that'll become useful.) Again, there tend to be more feats available than awarded.
Your starting deck consists of 15 cards. Its composition comes from a fixed set of quantities and boon types that comes with the starting character (Kyra has three spells and one Item, Merisiel has zero spells and six items, etc). As you progress, you can earn "Card Feats" that will let you choose to increase the quantity of one boon type by one. This increases your starting "health" by one and is generally highly prized. Each character has 10 possible upgrades, but again, Card Feats are few and far between.
The actual make-up of your starting deck can change every single scenario. The numbers and types don't change (unless you get a Card Feat), but the individual boons do. Before you start your first scenario, you can build your deck from any boons with the "B" deck number that have the "Basic" trait on the left side. Otherwise you get the "default" deck (which, in most cases, I find horrible). After a Scenario, you go through the boons you've acquired, plus the cards you started with (minus any you've banished) and rebuild your fifteen (or more) card deck. You can trade freely with the other characters, and everything you don't end up using is returned to the game box. I'm told you can freely pull from those same Basic boons each time you rebuild your deck up until you complete Black Fang's Dungeon and/or start on Attack on Sandpoint, but I've never checked. After that point, you only get to choose from Basics when you've ended a Scenario and, from among all the characters who played, there aren't enough boons of a single type to build your deck (if you banished more spells than you acquired, for example). Once you've been playing for a while, there are certain boons that you will rabidly try to acquire, like the Holy Light spell for clerics and bards, or the Deathbane Light Crossbow +1 for anyone whose Dexterity is better than their Strength...
As I said above, you always have unlimited access to Kyra and Merisiel. The other nine (Lem the Bard, Valeros the Fighter, Harsk the Ranger, Seoni the Sorcerer, Ezren the Wizard, Amiri the Barbarian, Lini the Druid, Sajan the Monk, and Seelah the Paladin) can be purchased with in-game gold (which can, in turn, be purchased with real cash, or earned by playing relentlessly). If you get the "Character Add-on Deck" (listed in the store), you get the last four I listed bundled in. If you get the Season Pass, you immediately get all eleven characters, all the boons in the Character Add-on Deck access to all the Adventures (7 total, B thru 6) as they are released, and some promo cards (boons and banes, I believe), which seem to be exclusive to the Season Pass.
You can have multiple iterations of each character, as near as I can tell. Basically, you can start a party fresh with un-advaced characters and basic decks, or build parties with advanced characters, though I haven't messed with that much.
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Location-base strategy...
As I mentioned, the first thing I consider when I start thinking about sending a character to a given location is, "which character is best able to meet the closing condition?" For example, the Wooden Bridge required a Dexterity or Stealth check to close, so Merisiel's my best option for that.
Next, I consider the banes and boons in the location deck and see who might be best to defeat/acquire them. For example, the Academy has a lot of Spells. Lem has both Arcane AND Divine skills, and thus wouldn't be bad there...
Sometimes, the "While at this location" condition might be something like, "At the start of your turn, succeed at a Constitution or Fortitude 90 check or die a horrible, painful death" (I don't have an actual example in front of me, so I rely on hyperbole.) I might send my character who has the best Constitution or Fortitude to that location, even if they were otherwise poorly suited to deal with those banes/boons at and/or close that location.
There isn't much more to day about bunching your party up. If you're all at the same location, then each character can give one card to one other character at the beginning of every turn. But that only works between characters at the same location. Similarly (I haven't tested this in PA, but in the physical card game) when it comes time to temp-close a location, EACH character at an open location can opt to take a crack at the "To close" condition until someone succeeds. Some boons can apply to the character playing it OR anyone at their location (potions, especially, can be used that way). But some banes do damage to everyone at a given location. Some things cause everyone at a location to summon and encounter a bane. And if everyone spreads out, you can win the Scenario more quickly once you close two locations, because if one of you encounters the Villain, you have enough people to temp-close ALL the other locations, leaving it no escape if it's defeated, and only one place to which to escape if it isn't. Knowing where the Villain is helps tremendously. So, these are all things to consider when you build your strategy. I'm playing a game with Lem, Seoni, and Merisiel using the physical cards, and we've had REAL trouble keeping Seoni alive. So, our plan next time is for Lem to hang with Seoni and use his Bard Song power to recharge cards left and right to help her checks while also making sure she's an optional target for his Cure spells, while Merisiel goes off alone where she can use her Back Stab with impunity.
Ok, if there's a max-post-size, I've probably tripled it. Now to see if everything I've said has been explained more concisely while I was typing up this novel...