Twinblade Paladin

If Twinblade Paladin is dealt lethal damage at the same time that you gain life, it won't receive a counter from its first ability in time to save it.

If you're dealt first-strike combat damage that brings your life total below 25, Twinblade Paladin will immediately lose double strike. It won't deal regular combat damage unless you bring your life total back above 25 before the regular combat damage step.

If you gain an amount of life "for each" of something or "equal to the number" of something, that life is gained as one event and Twinblade Paladin's first ability triggers only once.

If Twinblade Paladin gains double strike after combat damage has already been dealt (most likely because a creature with lifelink dealt combat damage), Twinblade Paladin will deal only regular combat damage.

In a Two-Headed Giant game, life gained by your teammate won't cause the first ability to trigger, even though it caused your team's life total to increase.

In a Two-Headed Giant game, Twinblade Paladin has double strike as long as your team has 25 or more life.