If “Ante” is the only card in your hand, you cannot activate it.
If your opponent has no cards in his hand, you cannot activate “Ante”.
You select cards at the resolution of “Ante”’s effect, not at “Ante”’s activation.
You cannot chain “Barrel Behind the Door” to “Ante” because you don’t know for certain whether you will take damage.
If either player chains “Raigeki Break” or “Last Turn” to “Ante” and then has no cards at resolution of “Ante”’s effect, “Ante”’s effect disappears.
When “A Legendary Ocean” is active and you activate “Ante”, when you check the Level, treat the Levels of WATER monsters in the hand as 1 lower for purposes of “Ante”.
Netrep Rulings:
If “Cost Down” has successfully resolved before “Ante” resolves, the monster chosen by the player who activated “Cost Down” is reduced by 2 Level Stars as per the effect of “Cost Down.”