Activate Urza, Prince of Kroog by paying 4, creating a token copy of Training Grounds that is a 1/1 Soldier in addition to its other types.
Activate Urza, Lord High Artificer's first ability by tapping the Training Grounds token, adding .
Activate Urza, Prince of Kroog by paying 2, creating a token copy of Training Grounds that is a 1/1 Soldier in addition to its other types.
Activate Urza, Lord High Artificer's first ability by tapping the Training Grounds token, adding .
Activate Urza, Prince of Kroog by paying 1, creating a token copy of Training Grounds that is a 1/1 Soldier in addition to its other types.
Activate Urza, Lord High Artificer's first ability by tapping the Training Grounds token, adding .
Repeat from step 5.
This ingenious assembly transforms ordinary permanents into a playground of cost-reduction and mana generation, anchored by Encroaching Mycosynth turning everything you own into artifacts. With those permanents now fitting the bill, Urza, Prince of Kroog can target Training Grounds with his copying ability. Because Training Grounds is a creature thanks to that same Mycosynth, its own discount ability applies to Urza, Prince of Kroog, shrinking his activation cost down to just a single mana. From there, Urza, Lord High Artificer steps in to tap the newly created Training Grounds tokens for blue mana, fueling an endless loop that floods the board with infinite creature enters-the-battlefield triggers and a massive army of tapped 1/1 Soldier artifact creatures.