The greed is just so excessive I can't be inclined to spend another dollar
Stealing a main phase is fun too, and you could do some powerful stuff with beginning phase
It offers excellent insurance against sweepers, which is nice, but the real value is in reusing Polukranos, World Eater, and to a lesser extent (oddly), Genesis Hydra or Nyleas Disciple
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of Emet-Selch of the Third Seat's first ability)
The Tenth Doctor EDHREC has The Tenth Doctor at #1, which may be in part because David Tennants Doctor is one of the most popular of the series
Use the mana value of the legendary creature that died as it last existed on the battlefield to determine what may be targeted with Havi's last ability