Crypt Rats Not Affected by Mutagenic Growht
As you can see in the screenshots, my opponent had a Crypt Rats on the field.
During his main phase he pays 5 mana for Crypt Rats but puts zero damage on the stack(That is weird already).
I let it resolve, and after that he uses all the 5 mana and puts 5 damage on the stack(now is for real).
I had a 4/4 creature on the field that I wanted to survive that with my mutagenic growth.
I cast Mutagenic Growth, it resolves making my creature 6/6 and the 5 damage from Crypt Rats resolve, killing everything but Akroan Skyguard. My 6/6 creature shouldn't be killed.
For this issue, please submit at: https://mtgo-support.wizards.com/hc/en-us/requests/new and select 'Reimbursement Request / Report An Issue'.