The only creature you have is a 2/2 black creature with protection from white. A green instant is played that allows one of your opponents to have one of their creatures fight one of your creatures. They choose to have a white 3/2 creature with double strike fight your creature.
Is this a legal target, and if so, how does the fight resolve?
It is a legal target, and your creature defeats the opponents creature.
The spell targeting your creature is green, not white, so your creature is a valid target, but the creature fighting it is white, so it cannot damage your creature.
A 6/6 creature with deathtouch and trample is blocked by a 2/3 creature with first strike and a 4/4 creature with no abilities. How much damage, if any, is dealt to the defending player?
4 damage.
Only 1 damage needs to be dealt to each blocker, allowing 4 excess damage to hit the player. The first strike is irrelevant in this scenario.
A 6/6 green creature with trample is blocked by a 2/2 creature with protection from green. How much damage, if any, is dealt to the defending player?
4 damage.
The attacker must still assign at least 2 damage to the blocker, even though that damage is prevented. The rest is free to be assigned to the defending player.
A 5/5 creature with deathtouch and trample is blocked by a 2/3 creature with reach and banding and two 1/1 creature tokens. Assuming damage is assigned optimally, how much damage, if any, does the defending player take?
No damage.
A creature with banding allows the blocking player to assign damage as they choose, up to the toughness of each blocker. They can assign 1 damage to each token, and 3 to their 2/3.