How do I identify which addon or plugin is causing a crash?

The binary search method is the most reliable approach for finding a problematic addon without testing each one individually.

First, note which addons were recently added or updated; start with those. Remove the most recent additions one at a time and restart after each removal. If removing one stops the crash, that addon is the cause.

If recent additions are not the issue, disable half of your addons by moving them to a temp folder (create a folder outside your addons/ directory and move half the addon folders into it). Restart and test. If the crash is gone, the problem is in the half you moved. If it persists, the problem is in the remaining half. Repeat: move half of the suspected group and test again. You narrow the culprit to a single addon in about 5-6 iterations for 50+ addons.

For Minecraft, the same approach applies to the plugins/ folder. The startup log usually names the offending plugin on crash; look for "Error enabling plugin" or a stack trace mentioning the plugin class. Remove that plugin and test.