Yes, it will resolve unless it's obvious it still needs the creature to be in play - destroying 'Hedron Crab' after its Landfall trigger goes on the stack will not stop the resolution. However if you destroy 'Scute Mob' before its trigger can resolve, clearly the effect will do nothing as the 'Scute Mob' is no longer in play to receive the +1/+1 tokens.
No, the flanking ability in Magic: The Gathering does not stack with other instances of flanking on the same creature.
While damage is still on the stack, the player who controls that creature has the opportunity to respond to the 'ping' by using the sacrifice outlet or any other instant or ability, if they choose to.
'Casting a creature spell' means to pay the mana cost and put the creature spell on the stack. If this is allowed to resolve, then the creature enters the Battlefield.
Normally, no, there is nothing to respond to. You resolve all parts of Flash's effect before you can put anything else on the stack. But if you want to pay the cost you can use the creature's mana abilities to pay for it, assuming it has haste or does not need to tap, mana abilities do not use the stack and can be used during the resolution of an effect.
Yes, the ability lifelink does stack with multiple instances on the same creature. Each instance of lifelink will trigger separately, allowing the creature to gain life equal to the total damage dealt by each instance.
In Magic: The Gathering, the stack is a zone where spells and abilities are placed before they resolve. When a player casts a spell or activates an ability, it goes on top of the stack. The last spell or ability put on the stack resolves first. Players can respond to spells and abilities on the stack by adding more spells or abilities. Once all players pass priority without adding anything to the stack, the top spell or ability resolves, and players can continue to resolve spells and abilities in order.
In Magic the Gathering, the 'stack' is the imaginary area where spells and abilities go when they are cast/played, and are waiting to resolve. So say one player casts a Lightning Bolt, targeting one of his opponent's creatures. He pays the mana cost and the spell goes on the 'stack'. The opponent however to save his creature, responds to this by casting 'Giant Growth' on that same creature. The stack goes by 'LIFO' order - last in, first out. It means that the latest object to go on the stack, will be the first to resolve. So Giant Growth will resolve first, and then Lightning Bolt. But say if Player A had some kind of counterspell, he could place that on the stack above Giant Growth to counter it and remove it from the stack, meaning ultimately the creature will die to Lightning Bolt. Tapping permanents to generate mana (be they land or anything else that can do it), a 'mana ability', does not use the stack, it is uninterruptable so can't generally be countered. Morphing, flipping a face-down Morph creature face-up, also does not use the stack, so a Morph cannot be quickly dispatched once the intention to flip is known. The stack can be interrupted as it resolves. Imagine a stack with objects A, B and C on it. When C resolves, either player might feel the need to play something else, so this will become object D on the stack above A and B, and will resolve before them.
In Magic: The Gathering (MTG), the stack is a zone where spells and abilities are placed before they resolve. Players can respond to spells and abilities on the stack by playing their own spells or abilities. The last spell or ability put on the stack is the first to resolve. This allows for strategic gameplay and the opportunity to counter or disrupt your opponent's plays.
If a card's not a land, then it's a spell - a creature on the stack waiting to resolve is a 'creature spell', for example. You can use a 'counter target spell' card against creature spells, instants, artifact spells, etc, the only things you can't use it on are lands, or activated abilities.
They are Creature Permanents while on the battlefield, Creature Spells while being cast on the stack, and Creature Cards at any other time. So when a player pays the mana cost on a creature card, putting it on the stack, it is now a spell and can be countered by anything that counters spells. After the spell resolves, it is just simply a Creature Permanent.
The ability of it does not stack.
Yes, it can protect a creature or player from an indirect source of damage, such as Pyroclasm. So when Pyroclasm is put on the stack, you add Master Apothecary's ability to it, choosing the target. You may do this as many times as you want, and have untapped Clerics to pay the cost with. Then each ability will resolve, setting up a condition on those targets to prevent the next two damage they would be dealt. Finally Pyroclasm will resolve - all creatures will take 2 damage, but those that Master Apothecary used his effect on, will prevent it.