[OP12-036] - Roronoa Zoro (Legacy of the Master)

What does "This card in your hand cannot be played by effects." mean?

It means that you cannot play this card using any effects that play cards from your hand, such as the [On Play] effect of "ST12-003 Dracule Mihawk". You can still play it from your hand by paying its cost as usual, and you can also play it using an effect from a place other than your hand, such as your trash.