My feelings are the same as you guys. If we look at the timeline: Jaga banished Grune Grune ended up on Third Earth after travelling many years in space Grune wreaked havoc on Third Earth Grune was killed/imprisoned Many centuries later, Grune's ghost was released X years after banishing Grune, the ThunderCats fled the destruction of Thundera. It took Y years for them to reach Third Earth. Soon after arriving, they encounter Grune's ghost. As Booshman said, Jaga piloted the ship almost the entire journey. If we assume that Jaga was maybe 70 years old when they started the trip, we could say that the trip was about 20 or 30 years long. So it doesn't coincide with Grune being dead for centuries as X + Y is unlikely to be equal to many centuries. The only way that Grune being dead for centuries would not be a continuity error is if the ThunderCats' have very long lifespans. Maybe they live for thousands of our years. Which reminds me of a line of dialogue that Loki says to Odin in "Thor The Dark World".