Delta is offering a 50% bonus on transfers of mileage from one account to another by January 31.
The most miles you can transfer at a time is 30,000 and the cost is 1 penny per mile plus $30. You can thus ‘buy’ 15,000 bonus miles for $330.
Not worth it to me, I won’t ever do this for a bonus of less than 100% (which they’ve offered in the past) just for the sake of accumulating miles.
On the other hand, if you’re short miles for an award and you have a friend or spouse with some orphan miles this is one way to top off towards a specific redemption.