A card is considered to have been printed at common if the Wizards of the Coast Gatherer lists it as a common
Hear me out before hopping into the comments
Perhaps theres a niche home for the card in Old School or AB40 (where banding is actually quite good)
Plus, decks centered around Titania, Protector of Argoth or other legends that reward you for sacrificing lands can turn this cards additional casting cost into a benefit
Having such consistent access to a powerful effect makes this an excellent Simic token commander that gives your deck far more consistency than you could hope for with it in the 99
If an activated ability of a creature you control costs no generic mana to activate (for example, if it costs , it costs, or it costs only nonmana actions such asor "Sacrifice a creature"), Training Grounds simply won't affect it