A propaganda technique that combines strawmanning with controlled opposition, most often used as a way to prevent or counter the excessive spread of evidence or theories that might put in danger the official narrative; it consists in makin up a blatantly false or fallacious anti-narrative claim/theory and then refuting it in order to smear all subsequent attempts at falsifying the narrative.
This technique works in three phases:
1) First, the organizers (propaganda agencies) manufacture a claim or theory that appears to contradict the officially accepted version on a particular issue, while at the same time being either blatantly fallacious on a logical level, or easily refutable by directly available evidence.
2) Second, that claim is launched through non-official channels (some anonymous source, "alternative" news sites, blogs or social media accounts, etc.) and allowed to go viral as much as possible without intervening, or even actively contributing to its spread.
3) Third, once the claim has now become widespread, mainstream official channels and talking heads are finally allowed enter the scene and debunk it with no chance for survival.
In this way, by association, any form of disagreement around the initial issue is brought down together with the false claim, making it way more difficult for alternative researchers to have their opinions considered.
The first phase serves to depict dissenters as the most stupid or guillable people as possible, by attaching the most easily debunked claims as possible to them, while the second one serves to make sure this blackwashing reaches the highest possible number of people and is therefore ingrained as much as possible into the popular imagery.