One of the worst ones I can remember in the SHL is someone gave up a draft pick for what turned out to be a bust, and that pick turned in to Avakael's first gen. He ended up playing his entire career with Buffalo, set a ton of records and as a user what the fantasy league what it is today. One of many Stampede trades that went in their favor. Obviously there's a risk anytime you trade away an early 1st round pick, but this one was very glaring because the player the team got back went inactive shortly after.
As for my sens the Zibanejad for Brassard deal is a bad one. I didn't like it at the time, and it's only gotten worse. It doesn't help I bought a Zibanejad jersey after he was drafted so now it's just another ex-Senator I have in the collection. On the plus side people don't ask me who he is anymore since he's a top player on the Rangers haha.