This page details bugs of DuckTales (NES).
There are a few more bugs documented here.
Endless Boss Fight
After defeating the Yeti in the Himalayas, if you pogo-jump into the snow and touch the treasure at the same time, the level will not end properly. The end-of-level music jingle will play and you'll collect $1,000,000, but the timer will continue to tick down and you'll be stuck in the boss room with nowhere to go. The only way out is to either reset the game or wait for the timer to run out. Note that doing the latter will allow you to fight the Yeti and collect the treasure again, which essentially means you can convert each of your remaining lives into $1,000,000 if your timing is good enough.