Activate the creature with Elemental Mastery attached by tapping it, creating a number of 1/1 Elemental creature tokens with haste equal to its power.
Activate Phyrexian Altar by sacrificing an Elemental.
When the Elemental dies as an artifact due to Mycosynth Lattice, Dross Scorpion triggers, untapping the creature with Elemental Mastery attached.
Repeat.
By transforming every permanent into an artifact, Mycosynth Lattice turns your entire board into fuel for Dross Scorpion's relentless untap trigger whenever anything perishes. You channel this engine through Phyrexian Altar, sacrificing the hasty tokens generated by Elemental Mastery to continuously refund your mana while feeding the Scorpion's metal-craft. Because Dross Scorpion neatly untaps your enchanted creature in response to each sacrifice, you can tap it repeatedly to flood the board with new tokens and cycle the loop infinitely.