Activate Marneus Calgar by paying 6, creating two 2/2 Astartes Warrior creature tokens.
When the Astartes Warriors enter the battlefield, Marneus Calgar triggers, causing you to draw a card.
Activate Lotus Ring's equip ability by paying 0 due to Puresteel Paladin, attaching it to an Astartes Warrior.
Activate the Astartes Warrior with Lotus Ring attached by tapping and sacrificing it, adding 3.
Repeat from step 3 for the remaining Astartes Warrior.
Repeat from step 1.
This clever engine centers around Marneus Calgar, whose activated ability creates two Astartes Warrior tokens that instantly trigger his own card-drawing prowess. Puresteel Paladin makes this loop possible by granting metalcraft support that reduces the equip cost of Lotus Ring to zero, allowing you to freely arm the newly minted tokens. Once equipped, those same tokens can be sacrificed directly to Lotus Ring's ability for mana before you loop the entire sequence. Meanwhile, Tannuk, Steadfast Second and the rest of the board state sit ready to capitalize on the resulting cascade of triggers and card draw.