How the golem works is like so:
-On my turn, I tap four mana and play Lodestone Golem. I pass my turn.
-On your turn, you tap five mana and play Bloodbraid Elf (an extra colourless is required because of the golem's static ability). You get to cascade. You reveal a Sprouting Thrinax and because it's cmc is less than BBE, you get to cast it for free. However, because of the golem you must now also pay an additional 1 colourless for the thrinax. If you are unable to pay then the thrinax can not be cast and must be placed on the bottom of your library.
Lodestone Golem could have been the answer to Jund decks, if only it had greater than 3 toughness.