Priority Bug on Harrowing Swarm
https://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=673594
According to the rules detailed here, I should be able to turn the creature up once I have priority. However, during the game, even though I had sufficient mana to do so, the game did not give me priority on my opponent's turn to activate the ability. Harrowing Swarm was supposed to reduce the mana cost for the ability, but the game didn’t allow me to turn it on as expected.
2
votes

-
DAC169#34537 commented
There are cards that can stop such things, like Karlov Watchdog. Did your opponent have any of them?