Arna Kennerüd, Skycaptain

Flying is an evasion ability.

A creature with flying can’t be blocked except by creatures with flying and/or reach. A creature with flying can block a creature with or without flying. (See rule 509, “Declare Blockers Step,” and rule 702.17, “Reach.”)

Multiple instances of flying on the same creature are redundant.

Lifelink is a static ability.

Damage dealt by a source with lifelink causes that source’s controller, or its owner if it has no controller, to gain that much life (in addition to any other results that damage causes). See rule 120.3.

If an object changes zones before an effect causes it to deal damage, its last known information is used to determine whether it had lifelink.

The lifelink rules function no matter what zone an object with lifelink deals damage from.

If multiple sources with lifelink deal damage at the same time, they cause separate life gain events (see rules 119.9–10).

Multiple instances of lifelink on the same object are redundant.

Ward is a triggered ability. Ward [cost] means “Whenever this permanent becomes the target of a spell or ability an opponent controls, counter that spell or ability unless that player pays [cost].”

Some ward abilities include an X in their cost and state what X is equal to. This value is determined at the time the ability resolves, not locked in as the ability triggers.

Doubling a creature’s power and/or toughness creates a continuous effect. This effect modifies that creature’s power and/or toughness but doesn’t set those characteristics to a specific value. See rule 613.4c.

To double a creature’s power, that creature gets +X/+0, where X is that creature’s power as the spell or ability that doubles its power resolves. Similarly, an effect that doubles a creature’s toughness gives it +0/+X, where X is that creature’s toughness. Doubling a creature’s power and toughness gives it +X/+Y, where X is its power and Y is its toughness.

If a creature’s power is less than 0 when it’s doubled, doubling that creature’s power instead means that the creature gets -X/-0, where X is the difference between 0 and its power. Similarly, if its toughness is less than 0 when doubled, it gets -0/-X. If one characteristic’s value is negative but the other isn’t when both are doubled, it gets -X/+Y or +X/-Y, as appropriate.

To double a player’s life total, the player gains or loses an amount of life such that their new life total is twice its current value.

To double the number of a kind of counters on a player or permanent, give that player or permanent as many of those counters as that player or permanent already has.

To double the amount of a type of mana in a player’s mana pool, that player adds an amount of mana of that type equal to the amount they already have.

To double an amount of damage a source would deal, that source instead deals twice that much damage. This is a replacement effect.