When it's defeated, exile it, then cast it transformed.) When Invasion of Segovia enters the battlefield, create two 1/1 blue Kraken creature tokens with trample
Mutable Explorer's Mutavault Mutable Explorer is odd on it's own and it enters with a Mutavault
If you like these, you might even consider Gamble
Attacking and blocking creatures remain such until the combat phase ends, or until they are removed from combat for any reason
The only question you need to ask is, How many times do you need to flicker a couple key cards before your opponent has no chance of catching up? Im fairly certain that three times is often the death knell
That said, The War Doctor becomes a force of destruction with very little help from cards such as Ryan Sinclair, Act of Authority, and Valakut Exploration