I’m not sure how easy it would be to extend Discobot with more functionality, the logic lives inside https://github.com/discourse/discourse/tree/master/plugins/discourse-narrative-bot and doesn’t look like it was designed to be easily extended.
What you CAN do though is create some new ‘bot’ users and hook them up to external chatbots, have a look at Hubot Adapter for Discourse for instance!
Using Hubot as a starting point gives you an enormous amount of example scripts to look at and it’s pretty easy to cobble together your own completely custom code.