Need .last() functionality for categories – .last() will be deprecated going forward I have a matrix block that calls a category channel. The categories are nested three levels "deep" at times. I want to select first, second or third level links as needed.

When I use .last(), I can get the full url path to return. When I use .nth(n), I have to specify a value, which automatically limits the link path to that level of "deepness". 

What can I do to get the .last() functionality, without using .last()?

Note: .last() will be deprecated going forward in Craft 3 and beyond.
If you are not going to update your current project to Craft 3 (which will break nearly all your templates and all plugins anyway) you don't need to bother about that message. This is only for Craft 3 and not for Craft 2.

Otherwise looking in the docs might be a good idea. You can do

{% set query = craft.entries().section('news') %}
{% set total = query.count() %}
{% set last = query.nth(total - 1) %}


or 

{% set oldest = craft.entries()
    .section('news')
    .inReverse()
    .one() 
%}