Intruder Alarm and Maskwood Nexus on the battlefield.
Creatures you control can tap to produce at least ({3} magic symbol) .
Maskwood Nexus does not have summoning sickness.
({2} magic symbol) ({U} magic symbol) available.
Steps
Cast Bring to Life by paying ({2} magic symbol) ({U} magic symbol) , causing Maskwood Nexus to become a 0/0 artifact creature, then putting four +1/+1 counters on it and exiling Bring to Life.
Activate any number of mana-producing creatures you control by tapping them, adding at least ({3} magic symbol) .
Activate Maskwood Nexus by paying ({3} magic symbol) and tapping it, creating a 2/2 Shapeshifter creature token.
When the Shapeshifter enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Repeat from step 2.
If creatures you control can tap to produce at least ({4} magic symbol) , this combo nets infinite mana.