When defending Forge of the Fluft in a showdown, can I tap the legend to use Long Sword in my base?

Ruling: No, you cannot use the ability granted by Forge of the Fluft during a showdown. The ability is an activated ability with default timing, which can only be used during your own turn, in an open state, and not during a showdown.

Nuances:

• You also cannot use this ability on your opponent's turn, even outside of a showdown
• The ability can only be activated during your own Main Phase when the game is in an Open State
• This is distinct from playing Long Sword directly from hand using its Quick-Draw keyword, which does have Reaction timing and can be used during showdowns