Set up a 'retrospective mailbox' at the beginning of the iteration. Whenever something significant happens or someone has an idea for improvement, they write it down and 'post' it. (Alternatively the 'mailbox' can be a visible place. This can spark discussion during the iteration.) Go through the notes and discuss them. A mailbox is great for long iterations and forgetful teams.
Different parties present manifestos for change. Who will get your vote? Source:
Is there an election coming up in your country? Use it as a back drop for your team to convince each other of their change initiatives.
Ask the participants to split into political parties with 2 or 3 members. For 20 minutes, each party will work on a manifesto for change. What isn't working? How would they improve things? Afterwards the parties meet again and their leaders present their manifestos. Be prepared for tough questions and heckling! Now plan for a better world! Summarise the manifestos with sticky notes, one color per party. What do the parties agree on? Which promises are unrealistic and which can you achieve?
Let team members appreciate each other and end positively Source:
Agile Retrospectives who took it from 'The Satir Model: Family Therapy and Beyond'
Start by giving a sincere appreciation of one of the participants. It can be anything they contributed: help to the team or you, a solved problem, ...Then invite others and wait for someone to work up the nerve. Close, when no one has talked for a minute.