{T}: Add {C}{C}.
{2}, {T}, Sacrifice this artifact: Exile any number of target players' graveyards. Draw a card.
You choose any number of target players as you put Stonespeaker Crystal's ability on the stack and exile their graveyards as it resolves. You may not target a player and then choose not to exile their graveyard.
You may choose to target no players while activating the last ability if you just want to draw a card.