After some decks arose with Soul Warden and Soul's Attendant and lifegain payoffs to go with them, these creatures that reward more creatures with lifegain have become colloquially known as soul sisters. Table of Contents show What Are Soul Sisters in MTG
Swarmyard is an incredibly powerful utility land balanced out by two factors: It only taps for colorless mana and works only with a specific subset of under-supported creature types
We are also just looking at cards from the main set and not the most valuable cards from the Bloomburrow precons
That scarcity, paired with the marquee Pokmon they depict, keeps the MHR at the peak of every sets want list for collectors
If Council of Reeds leaves the battlefield before its triggered ability resolves, the token will still enter as a copy of Council of Reeds, using Council of Reeds's copiable values from when it was last on the battlefield
The Wailord card from the Vivid Voltage expansion is a great example of this