Once it dies, you'll likely be drawing more than one card, more than replacing what you lost in terms of resources
Luckily, there are means of circumventing this drawback, such as the card Conjurer's Closet, which allows you to blink any of your creatures, washing them of their Nightmare typing before they'd be exiled from Chainer's death
On the first turn you drop [casthaven]Dragon Throne of Tarkir[/casthaven], its a colorless oversized-[casthaven]Overrun[/casthaven], and every turn after its just gravy
Blue doesn't have solid removal access outside of cards bouncing any permanent - which are usually on spells, not creatures
Shes also extremely good for combining with other sweeper resistant gameplans, giving you a reliable source of follow-up threats that are all too happy to pick up a machete for the cause
Many EDH cubes allow players to start with a copy of Sol Ring, Command Tower, Commander's Sphere, and The Prismatic Piper to help decks along and give a commander feel