The abilities are separate and cumulative. If another creature you control is both of the listed colors, it will get a total of +2/+2.
Multiple Murkfiend Lieges are redundant when it comes to the untap effect. You canâ€™t untap your permanents more than once in a single untap step.
During each other playerâ€™s untap step, effects that would otherwise cause your green and/or blue creatures to stay tapped donâ€™t apply because they only apply during *your* untap step. For example, if you control Nettle Sentinel (a green creature that says â€œNettle Sentinel doesnâ€™t untap during your untap stepâ€), you untap it during each other playerâ€™s untap step.
All your green and/or blue creatures untap during each other playerâ€™s untap step. You have no choice about what untaps. Those creatures untap at the same time as the active playerâ€™s permanents.
BUY THIS CARD