JQL Tricks plugin enhances the search functionality in Jira. It is supported on both Jira Datacenter and Cloud but works differently on both the versions, due to the architectural differences of the App framework.
On Jira Datacenter, JQL Tricks plugin adds a set of useful JQL functions. The app exposes more than 50 functions, including simple issue functions to complex issue linking & hierarchy functions.
On Jira Cloud, JQL Tricks plugin adds a set of JQL aliases that can be used in JQL queries. These aliases are similar to the standard JQL fields in Jira and duplicates the functionality of complex JQL functions in the Jira DC version.
Copy to Subtask plugin lets you copy the custom field values from parent issue to its subtasks on creation.
There are minor configurations available using which you can limit this functionality to selected issueTypes and Custom Fields. You can also optionally hide the custom fields that are to be copied from the create subtask screen. Without this, the value will be auto populated from the parent on the screen and can then be overwritten!