Deletes itself

Modifies Watchdog functionality

Malware like Mirai modifies the Watchdog to prevent it restarting an infected system.

Creates/modifies Cron job

Cron allows running tasks on a schedule, and is commonly used for malware persistence.

Modifies init.d

Adds/modifies system service, likely for persistence.

Modifies rc script

Adding/modifying system rc scripts is a common persistence mechanism.