Not allowing instant speed
During gameplay, I was unable to cast tailswipe at instant speed during my turn or opponents. I had mana available and no other cards were preventing instant speed spells.

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Swan#32377 commented
I have one instance attached. I had Venerated Rotpriest (green) blocking an opponent. I had two mana down, a tapped forest (from casting Rotpriest) and an untapped Thornwood Falls (green/blue). I declared Rotpriest as a blocker, then was unable to cast my spell (Slip Out the Back - one blue) to save him. This resulted in me losing Rotpriest and eventually the game.
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Swan#32377 commented
Similar thing has happened to me multiple times and has lost me the game each time as well.
I have one instance attached. I had Venerated Rotpriest (green) blocking an opponent. I had two mana down, a tapped forest (from casting Rotpriest) and an untapped Thornwood Falls (green/blue). I declared Rotpriest as a blocker, then was unable to cast my spell (Slip Out the Back - one blue) to save him. This resulted in me losing Rotpriest and eventually the game.
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Marty#40362 commented
During gameplay, I was unable to cast at instant speed during my turn or opponents. I had mana available and no other cards or creatures were preventing instant speed spells. I cant play like this