From: https://github.com/mattermost/mattermost-server/issues/10463

Please allow incoming webhooks to use response_type. I'm looking at making a bot that would allow others to roleplay. This bot functions by watching the channel, and when it sees a message with a trigger that has been set up with it, uses a incoming webhook to post a message with a custom picture and username before deleting the triggering message.
This gives the effect of someone being able to play different characters, especially when paired with: https://mattermost.uservoice.com/forums/306457-general/suggestions/37237117-allow-webhooks-to-post-to-reply-threads