Spawning of Fire Mage entity makes my Aternos server to crash. I kept killing that specific entity to stop my server from crashing but still it keeps spawning naturally.

Crash log:
Crash Log.txt

Closing all bug related issues as I just pushed a big update. (many changes to the code)
If the issue is still there, please create a new issue and provide new log files.

The 1.8 update is currently BETA which means it's not ready for stable worlds. If you are playing multiplayer I suggest you wait for a release candidate.