Bypass AMSI by patching AmsiScanBuffer two different ways.
jmp.cs places a mid-function hook in AmsiScanBuffer. A relative jmp instruction is used to jump to the end of the function & return 0 (AMSI_RESULT_CLEAN).
ret.cs places a hook at the beginning of AmsiScanBuffer to return 0 (AMSI_RESULT_CLEAN).
Credits to: Rasta Mouse for some of his code and some of his ideas.
I'd recommend compiling with Visual Studio and at least .NET 3.5. Use a class library (C# dll) template. Load into PowerShell.exe using your preferred method. Execute with [Bannana]::Peel().