Duergar Mine-Captain does not have summoning sickness.
({1} magic symbol) ({RW} magic symbol) available.
Steps
Declare Duergar Mine-Captain as an attacker.
Activate Duergar Mine-Captain by paying ({1} magic symbol) ({RW} magic symbol) and untapping it, causing all attacking creatures to gain +1/+0 until end of turn.
Activate Duergar Mine-Captain by tapping it, adding three mana of ({R} magic symbol) or ({W} magic symbol) .
Repeat from step 2.
Results
Infinite colored mana that can only be spent during combat phase.