First, if a character with Range and a character with a "When attacks" ability both attack, then both abilities would enter the queue. The attacking player would be able to resolve the abilities in the order of their choosing, correct?
No. The attacking player would decide the
order of entry into the queue, which determines the
order of resolution. Once abilities are in the queue, you cannot decide which one you will resolve before another.
Assuming I could choose to use a "When attacks" ability before resolving range damage, when should Range damage enter the queue?
The dealing of damage from Range is part of its ability and it would need to resolve completely before you proceed to any subsequent ability in the queue.
Does the character need to be active when the attack is initiated or when Range damage is being assigned?
Assuming in this question you mean the Character die with Range needs to be active.
Yes, when the attack is initiated. No, when Range damage is dealt.
In most cases, a character die must be active for its ability to trigger then enter the queue (abilities that state “character does not need to be active” are obvious exceptions). When an ability enters the queue, the game state is noted, and that ability will be resolved against that game state. If the resolution of an ability alters the game state (this includes the removal of the die that placed its ability into the queue), this new game state does not affect the resolution of subsequent abilities already in the queue.
The application of Range establishes a unique situation. Not only is there the dealing of damage from the initiating die with Range (and any other dice with Range) the Active player has, but also a simultaneous dealing of damage from any dice with Range from the Inactive player. These two applications of damage are coupled and once both players’ dice deal their damage, the resolution of this ability is complete.
Suppose I attack with Anti-Monitor and Starfire. If I use Anti-Monitor's ability to KO Starfire, will she still be able to assign Range damage?
Yes. When you attacked with Anti-Monitor and Starfire, their abilities triggered simultaneously, since both abilities have “when attack” triggers. At this point, you determine the order of entry into the queue and the game state is noted. When you resolve Anti-Monitor’s ability and KO Starfire, her ability is still in the queue pending resolution.
If I don't KO Starfire, but Anti-Monitor's ability causes all opposing characters with Range to be KO'd, will my opponent still assign Range damage from the characters that were KO'd by something other than Range?
Yes. Any other dice with Range that are KO’d by Anti-Monitor would be able to deal their damage. Because of the unique application of Range (as stated above), the Range ability of these opposing dice were pulled into the queue along with Starfire.
Suppose my opponent has multiple characters active with one Brainiac 5 active. I attack with Starfire and Spider-Man. First I use Spider-Man to spin their Brainiac 5 to an energy face, then activate Starfire's Range. Would my opponent's dice still be able to assign Range damage even though they've lost the ability once Brainiac 5 is no longer active?
Yes. Brainiac’s ability is setting a game state where all of the Active dice on his team have Range. This game state is checked when Spider-Man and Starfire attack and their abilities entered the queue.
Once Starfire entered the queue, her Range ability also pulled the opposing dice with Range into the queue. Even though Spider-Man’s ability removes Brainiac’s Range gaining ability, the game state was these dice had Range when Starfire entered the queue. Therefore, your opponent’s dice will deal their Range damage.
