Cast Worm Harvest for its retrace cost by paying 2B/GB/GB/G and discarding a land card from your hand, creating at least eight 1/1 Worm creature tokens.
Activate Phyrexian Altar seven times by sacrificing seven Worm tokens, adding 3B/GB/GB/G.
Activate Groundskeeper by paying 1, returning a basic land card to your hand from your graveyard.