Floating Mana?

[Bofu]

Ok, so my opponent is resolving Blood Moon, I have Abrupt Decay available in hand and Mana to cast it. How do I float GB, let Blood Moon resolve and then cast Abrupt Decay targeting it?

This was an issue that happened earlier, thankfully my opponent was nice enough to concede since I drew the kill on my turn

[LevelX]

Ok, so my opponent is resolving Blood Moon, I have Abrupt Decay available in hand and Mana to cast it. How do I float GB, let Blood Moon resolve and then cast Abrupt Decay targeting it?

This was an issue that happened earlier, thankfully my opponent was nice enough to concede since I drew the kill on my turn

Use the right mouse button while your mouse pointer is located in your battlefield .
A context menu will open. Uncheck the "Pay mana automatically" option.
If the option is set to off mana in the pool is only used to pay mana costs if you click the related mana symbol in the player mana pool.

But in your situation you can also simply tap the mana before Blood Moon resolves as long as you cast nothing else but/before the Abrupt Decay. You not even need that mana option in your example.

[emerald000]

Ok, so my opponent is resolving Blood Moon, I have Abrupt Decay available in hand and Mana to cast it. How do I float GB, let Blood Moon resolve and then cast Abrupt Decay targeting it?

This was an issue that happened earlier, thankfully my opponent was nice enough to concede since I drew the kill on my turn

Also, make sure to have a stop set in your opponent's main phase so you have priority to cast Abrupt Decay before your mana pool empties at the end of the phase.