To create a mediation group, select Mediation and then select CREATE MEDIATION GROUP. As this mediation group will target rewarded ad units, select Rewarded as the ad format. 


Select Android as the platform type and select CONTINUE. Next, enter a name for your mediation group. It should be descriptive, so you can find it in the mediation groups table later. We’ll name this Rewarded Android Japan South Korea. 


Next, under location, notice it defaults to targeting all countries and territories. Since you want this mediation group to target ad requests from users in Japan and South Korea specifically, select the option to target specific countries and territories. As you input the name of each country into the search field, it will be added to a list below. 


AdMob also gives you the option to exclude certain countries and territories for a given mediation group. 


Next, select the apps and rewarded ad units this mediation group will target by clicking the ADD AD UNITS button. Select the ad units you want to associate with this mediation group. In this case, this mediation group will target the ad units: Android Game 2.0 Power Up Pack and Android Game Extra Life Reward. When AdMob receives ad requests from the selected ad units, AdMob will try to match the requests to the mediation group or groups that target those ads. 


Select DONE.


Whenever you need to add additional ad units in the future, you can always come back and add to this group saving yourself time. 


Now it's time to add your ad networks, AdMob and another rewarded ad network. You’ll notice that AdMob is there by default and is optimized in the list of ad sources. Select ADD AD NETWORK to add a new rewarded ad network. 


The optimize option is enabled by default, allowing AdMob to manage the positioning of this ad network in the mediation chain. Specifically, AdMob will automatically make adjustments to the eCPM associated with the network based on traffic in your app, historical data, and information retrieved from the ad network itself. It’s worth noting, some ad networks may not support optimization and this option may not appear.


Alternatively, you can disable optimization and enter a manual eCPM from the third party’s reporting to use for this ad network. Remember, this is the eCPM AdMob will use to dynamically position the network in the mediation chain where it will compete with other ad sources to fill ad requests. 


Go ahead and leave optimization enabled and enter the credentials required by the ad network you selected. These credentials need to be obtained from the third-party network. If you've already used this ad network in another mediation group, you won't be asked for the credentials again.


Review and check the Authorization checkbox to authorize AdMob and Google to access your account. 


Enter $5 as the eCPM to use for this network until AdMob can gather enough data for optimization. This eCPM will be used to dynamically position the network in the mediation chain where it will compete with other ad sources to fill ad requests.


Select CONTINUE.


Enter the configuration details for each ad unit. In most cases, these details will be available in your account with the ad network. 


As this mediation group is targeting two of your apps’ rewarded ad units, you’ll want to create two corresponding rewarded ad units in the third-party’s UI and input the associated configuration details here in the mediation group. That way, when AdMob mediation considers a given ad request from these rewarded units, AdMob will pull in reporting for how that third party has been performing for each of them. We recommend having a 1:1 mapping between your AdMob ad units and the individual placements you create in each third party’s user interface. The more granular reporting allows AdMob to more accurately optimize the value for that ad network.


Select DONE. 


Now you can see both of your ad networks in what is referred to as a mediation chain or a mediation waterfall. 


Select SAVE to save this new mediation group. 


The new mediation group now appears in the mediation groups table.