And of Dan he said,
Dan is a lion's whelp,
Who leaps forth from Bashan (or ‘from the viper').
Moses finds little inspiration in some of the tribes and cannot arouse any prophetic enthusiasm about them. In Jacob's blessing Dan was the snake. Here he is to leap forth from the snake like a young lion. This may mean that the Danites will develop more strength, transforming from snake to young lion, or it may suggest that while having some strength like a young lion, they will shy away from ‘snakes'.
The ancient word bashan may well be parallel with the word btn at Ugarit where it meant a snake. Or the thought may simply be that the lions of Bashan were seen as particularly dangerous (these being the only ones they had encountered since reaching the land). Compare Song of Solomon 4:8 for abundance of lion's dens there.
Dan did not leap forth from Bashan against Laish, they went from the lowlands under the Philistines. Dan is never connected with Bashan in any way. It is just possible that they may have travelled through parts connected with Bashan to reach Laish but they may equally have gone through Naphtali if they wanted to surprise Laish. Compare Genesis 49:17 where Dan will ever be tricky but fearful.