Proliferate and Impending
The default option for proliferate with opponents permanents with impending from duskmourn is not to put counters on them. You can still put counters on them with proliferate but a nice QoL improvement would eb having the counters put on opponents impending permanents by default, like poison counters on opponents.
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Evu#00213 commented
I noticed this too. Arena is smart enough to select battles you protect for proliferation, even though they're owned by your opponent. I expected it to do the same for opponents' impending permanents and was surprised that it doesn't.