Here are the cards I found on the MTGNews rumor board, I think they are quite believable. The first 2 are from an Odyssey poster, and the latter 2 are inserts for gaming mags (e.g. InQuest).
Seize the Day 3R
Sorcery
Untap target creature. After this phase, there is an additional combat phase followed by an additional main phase
Flashback 2R(You may play this card from your graveyard for its flashback cost. Then remove it from the game.)
Rare
Illus: Greg Staples
Krosan Beast 3G
Creature - Squirrel Beast
Threshold - Krosan Beast gets +7/+7. (You have threshold as long as seven or more cards are in your graveyard.)
Those who see the squirrels go underground in the winter aren't ready for what emerges in the spring
1/1
Rare
Illus: Kev Walker
Firebolt R
Sorcery
Firebolt deals 2 damage to target creature or player.
Flashback 4R(You may play this card from your graveyard for its flashback cost. Then remove it from the game.)
Common
Illus: Ron Spencer
Mystic Zealot(???) 3W
Creature - ???(Cleric Soldier is my guess)
Threshold - Mystic Zealot gets +1/+1 and flying. (You have threshold as long as seven or more cards are in your graveyard.)
2/4
Common
Illus: Paolo Parente
Seize the Day - Relentless Assault? Cute, but...
Krosan Beast - My GOD. A 8/8 for 3G?! Threshhold is easy to achieve!
Firebolt - Good as an Instant. As a Sorcery, sucks donkey balls.
Mystic Zealot - Very nice. I think I'm gonna like Threshhold...
As for the cards, we're still not entirely sure how accurate they are. Shade's been strangely absent, and pwrchild is refusing to divulge any information. As such, R-elf is left to deal with everything by himself. We should have something for everyone by the end of the week (Sunday-Monday)
Yeah I just noticed that shade2k1 disappeared from totally from everywhere... he is not coming here nor on mtgnews... pwrchild just has refused to give us a spoiler...
We will know about Odyssey on Pre-Release?
How about Morbid Hunger and Springing Tiger... I think that although Pillow Wasp made a fuss and slush on MTGNEWS.com they look true-ish
I don't think pwrchild is using such... er... strong language, but I'm thinking that there's pressure from the powers-that-be or something. Maybe pwrchild was bribed with a booster box to keep silent.
Regardless, I think it's fun that we don't know what's coming. This way we'll be forced to buy oodles and oodles of cards just to see how bad they suck!
pwrchild is experimenting, according to her. She has stated only that she wants to know how we react to having no information from her about an upcoming set.
(Which only serves to stregthen my belief that she's a WotC employee whos task is to leak information as a sales trick. )
I think the symbol is the orb thingy shown in the left booster pack from the ad, which is possibly the rumored powerful artifact which all those pitfighter are fighting for.