October 5, 2018 7:55 a.m.
Also note that since this is related to a fairly recent change in the rules, there are many planeswalker cards out there that weren't printed with "Legendary" on the type line. They've all received official rulings to count as Legendary and you can get any of them with Captain Sisay.
October 5, 2018 noon
To add a bit of additional information to the above, all planeswalkers have received errata so they now read "Legendary Planeswalker". So, while a majority of the planeswalkers ever printed will not have the word "Legendary" on the card itself, the Legendary supertype has been retroactively applied to those cards as well.
October 5, 2018 12:06 p.m. Edited.
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