When you exert it and wants to cast 2 creatures with the mana, is there a way to use it in both so they can have haste? I tried it and only one of them had haste, there's no separation of arena's mana and other mountain's mana
#Arena of glory
coarse belfry
deep depot
I'd suggest floating the Arena of Glory mana before casting the creature spells and then cast each creature spell by spending that mana first. Then you can either finish it the cost-paying process with the Auto button, or activating the mana abilities manually.
You can access unspent mana through the listed mana symbols below your avatar on Desktop Classic. For the Mobile version and its Desktop backport, there should be a tab labeled with a stylized M, next to your hand.