I just had an opponent use this against me, except the opposite was true. I was playing on iOS, opponent would spend all their mana playing out equipments, and then continue to to equip everything to creatures. The only mana rock they had was mox amber, and it had been tapped. Despite this, it did not cost them anything to equip things to their creatures. Very frustrating, I had kept the upper hand for most of the game and likely should have won if not for the bug. I believe the intent is that there is meant to be a floor to the equip cost (1), and it should not go any lower than that.
I just had an opponent use this against me, except the opposite was true. I was playing on iOS, opponent would spend all their mana playing out equipments, and then continue to to equip everything to creatures. The only mana rock they had was mox amber, and it had been tapped. Despite this, it did not cost them anything to equip things to their creatures. Very frustrating, I had kept the upper hand for most of the game and likely should have won if not for the bug. I believe the intent is that there is meant to be a floor to the equip cost (1), and it should not go any lower than that.