Thanks to the PR by @simonmartyr it’s now possible to send even more inspiring Slack messages (starting with v2.4.0 of the Slack step), like

or if something goes wrong

Simply specify the Image URL and Image URL - if build failed options of the step, and that’s all!
Example config:
- slack@2.4.1:
inputs:
- webhook_url: $SLACK_WEBHOOK_URL
- channel: '#test-channel'
- message: |-
Build Success ($BITRISE_BUILD_URL)!
*Keep up the good work!*
- message_on_error: 'Ouch, Build failed! Quick, check the details at: $BITRISE_BUILD_URL'
- image_url: https://media.giphy.com/media/XreQmk7ETCak0/giphy.gif
- image_url_on_error: https://media.giphy.com/media/ToMjGpx9F5ktZw8qPUQ/giphy.gif
Keep your builds Slackin’! 