If anyone could do it, it's unsurprising one of the original 151 could manage to command a high price in a set themed after Alola
If the checklist card is face up in a public zone, it should be set aside and the double-faced card or meld card that it represents should be used instead
If the triggered ability causes two Assassins to be created (due to an effect such as that of Doubling Season), Headsplitter becomes attached to one of them
Try City of Brass, Forbidden Orchard, Mana Confluence, Gemstone Mine, Aether Hub, Rainbow Vale, or Tendo Ice Bridge instead
It has no longer become a placeholder
This concept probably doesn't represent the optimal Vintage Monastery Mentor deck, but it does contain some very powerful interactions