Chosen of Markov // Markov's Servant — ruling 1

You can tap any untapped Vampire you control, including one you haven't controlled continuously since the beginning of your most recent turn, to pay the cost of Chosen of Markov's activated ability. You must have controlled Chosen of Markov continuously since the beginning of your most recent turn, however.

Chosen of Markov // Markov's Servant : règles, fonctionnement et interactions (MTG)

Chosen of Markov // Markov's Servant is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

, Tap an untapped Vampire you control: Transform this creature.

How it works : Chosen of Markov // Markov's Servant

Original English text — Wizards of the Coast / Scryfall

#1January 22, 2011· Wizards of the Coast
You can tap any untapped Vampire you control, including one you haven't controlled continuously since the beginning of your most recent turn, to pay the cost of Chosen of Markov's activated ability. You must have controlled Chosen of Markov continuously since the beginning of your most recent turn, however.
No other card is named in this ruling.