Timing: On my first hero's turn I cast anti-magic on wardens. I have 2 spell power and twilight talent, however the anti-magic spell is applied for 2 turns only (should be 5). Moreover, the magic immunity received was only 13% and after a few basic calculations we can see that the efficiency of the spell is also not affected (quite expected I guess):
Antimagic immunity formula: 100% * E/HP where E=110+60*Spell power (I have Expert Holy magic).
Effect on wardens should be 100% * (110 + 60*5)/(214*8) = 23.94% (rounded down to 23% probably).
Instead, 13% confirms this formula where 2 spell power is applied instead of 5: (110 + 60*2)/(214*8) = 13.43% (rounded down to 13%).
Thanks for looking into it !