Kiki-Jiki by tapping it, creating a token copy of the mana-producing creature with haste.
Activate the creature token by tapping it, adding at least ({U} magic symbol) .
Activate
Freed from the Real by paying ({U} magic symbol) , untapping
Kiki-Jiki.
Repeat.
Notes
The chosen mana-producing creature must tap to produce at least ({U} magic symbol) and not be legendary. If it taps to produce multiple mana, you will net infinite mana of the type(s) produced.