This is much, much smaller than the estimated print runs of sets today, which are more like 2.5 billion cards
Most of the lands with Threshold are pretty underwhelming, with the exceptions of Nomad Stadium (which is incredibly bad) and Cephalid Coliseum
Its not the activation of an ability, its a keyword ability that just allows you to cast the card from your graveyard
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So, what we really want to see on warp cards are good abilities triggering when the permanent enters, considering how this mechanic leads us towards playing a certain number of Flicker spells in order to access a way higher quantity of value
Of course, the really exciting part here is the ability to double your mana from creature sources