A player's ability to play lands is one of the most inherent actions to the game of Magic, so attach that to an absurdly powerful effect and you end up with this cool cat
Pokemon TCG can be played on any surface providing both players know where each card is meant to be placed
This four-mana 3/3 lets you mill cards and return lands from the graveyard to the battlefield, butit also makes it cheaper to activate any land abilities you have and makes land creatures you control stronger too
And as has been suggested by the aforementioned list of most valuable Pokmon TCG cards, this pattern generally repeats, meaning Secret Rares are consistently more valuable than other cards in this way
Altar's Reap gives two additional cards to your hand - hopefully you can sac a zombie token - if not, the Chant can place that sacrificed card straight back into your hand again
If that bench contains other Garchomp exes, its a great chance to get them ready to switch in and deal out Sonic Dive, which has you re-discard two Energies to do 120 damage to any of your opponents Pokmon, whether benched or active