The rumors have begun it seems, according to 'Dewman' on MTGSalvation who saw a poster at this local store, we get the following tidbits for the upcoming set.
Three cards pictured on the poster are speculated to be the Release promo, and the 2 faction-specific Prerelease promos. Glissa would be the Phyrexian faction promo.
![6 6](/images/productsymbols/6_icon.gif)
Rare
Artifact Creature - Thopter
At the beginning of your upkeep, if you control no other Thopters, return Thopter Factory to your hand and put five 1/1 colorlessĀ Thopter artifact creature tokens with flying onto the battlefield.
5/5
140/155
![Green g](/images/productsymbols/g_icon.gif)
![Green g](/images/productsymbols/g_icon.gif)
![Black b](/images/productsymbols/b_icon.gif)
Mythic
Legendary Creature - Zombie Elf
First strike, deathtouch
Whenever a creature an opponent controls is put into the graveyard from the battlefield, you may return target artifact from your graveyard to your hand.
3/3
?/155
Also, Battle Cry is a new ability. According to CaptainBlack, it is an attack trigger. Speculation would put it on the Mirrodin side of the factions, if it is faction-specific.