Poison can also be healed with Pokmon abilities or other cards, like items
As such, without some fancy trickery, like a full engine rebuild, you can only get away with using it once
Although the Leader has the major drawbacks of starting with 2 Life and being unable to attack, its [Activate: Main] effect makes up for it with its power
Its the same type of removal as Imprisoned in the Moon or Bound in Gold: An Aura that you attach to a permanent to make it unusable
We wanted it to do something you'd want to do first, and something green, so we made it an "impulse" spell (R&D slang for a spell that only looks at a limited number of cards from the top of your library and lets you take onein our quest to lessen shuffling, it's how we do a lot of "tutoring" these days) that got you a creature or land
Primeval counters have their effect whether or not Muraganda Eldrazi is on the battlefield