Being able to (potentially) cheat out cards like Worldspine Wurm, Shriekwood Devourer and Thunderfoot Baloth is nice, but there are some solid reprints, too
If it enters with counters, those counters are included
Sisays great for decks that want to assemble a particular combination of legendary cards, like Gaea's Cradle, Nykthos, Shrine to Nyx, or Elspeth, Sun's Champion
Having this buddy sat on the board will give virtual card advantage by the bucket load, too, and will force opponents to spend removal to solve your failsafes
This design is whats commonly referred in Magic: The Gathering terms to as a 'mana dork' - a creature whose sole job is to sit there and churn out mana for their controller to amass
That means from the stack by Dissipate, from in play like Swords to Plowshares, or from graveyards like Bojuka Bog