The Emojibots were robots who served as avatar interfaces to the sentient microbots, the Vardy. Their purpose was to ensure the humans on the off-world Earth colony Gliese 581d remained happy at all times. To monitor their moods, everyone wore a badge which reflected that persons mood through the language of emojis. Emojibots viewed unhappiness and grieving as anathema and would enlist the Vardy to kill those showing such negative emotions.
When the TARDIS arrives on the colony, the Twelfth Doctor and Bill are greeted by the Emojibots and given badges. After the Doctor comes to the shocking realisation that the colonists had been slaughtered and their bones used as fertiliser for the food supply, their resultant upset is picked up by the Emojibots