What is an example of a retroactive airdrop?

Could you provide me with an example of a retroactive airdrop in the world of cryptocurrency? I'm curious to understand how this type of distribution works and how it benefits the recipients. Is there a specific instance where a retroactive airdrop was implemented, and what was the outcome for those who received the tokens? Additionally, what are the potential risks and considerations that should be taken into account when participating in such an event?