It gets everyone, and if X is greater than 6-7, your opponents wont have many decisions to make
I dont expect Plague Mare to be as good as Goblin Chainwhirler, but it isnt far off and looks to be a wonderful option for aggressive black decks to have access to
In general you will want to avoid putting the cycling lands in decks with three or more colours of mana, since they dont help fix your mana in that scenario, and you dont want them in decks that have a lot of one-mana plays and are looking to curve out, since tapped lands are so punishing in decks like that
This card may technically be colorless but we all know its a green card, and both Conspiracy sets have tons of green creatures that synergize well with each other
However, one evolution line is not enough for a deck, so this particular build throws in another popular group of Pokmon: The Gardevoir evolution line