Wanted to share that Mistrise village is currently bugged. I've submitted a bug report to the Arena team, but wanted to raise awareness on this.
Recreation Steps:
1. Cast any spell while holding priority
2. Activate Mistrise Village and let the ability resolve.
3. Cast another spell after activating before the first spell resolves.
Expected result: Only the second spell should be uncounterable.
Actual result: the first spell becomes uncounterable as soon as step 2 is complete. Additionally the second spell from step 3 also becomes uncounterable.