Yep, he just sits there growing bigger each turn until you Windfury him later on for the insta-kill, but he does telegraph your intentions! Warlocks will have to sac something huge to Shadowflame to kill it (or Twisting Nether), Priests Mass Dispel, and Hunters could Deadly Shot it if they can get our board down to nothing but it. Will make a good minion to run alongside the eggs though - if they want to AoE to kill him early, they have to give us a 4/4 to do it, for example.
But if you think about it, the 0/2 egg that turns into a 4/4 upon death will be one of the highest priority silence targets. If you play the Baron and can kill the egg on the same turn, that's two 4/4s in addition to your 1/7 Baron, as early as turn 4 or 5. So since they can't control when you Baron, they have to silence the Deathrattle asap or risk you getting massive minion value from a 2 drop (whether you can or not is irrelevant, the risk is too high). This could snowball with AS, turn 2 egg, turn 3 Feral Spirits, turn 4 AS spirit on egg, turn 5 baron + rockbiter/lightning bolt egg, and now you have 2x 4/4, and 2x eggs waiting to die to spawn 4x 4/4? Dream scenario, obviously, but against non-priests thats a game ending snowball.
As for the 2x Deathrattle effect of the Baron - I wonder if this applies to his own Deathrattles? Ie, AS on him before killing himself off, do you get 2x Baron back? Would a single Loot Hoarder now be a 3 card draw? O_O
Regardless, the most likely combo for Shaman's is going to be Cairne into AS + Baron. You get 2x Cairne back, and 2x Baine. For three cards, best case assuming no silence/transforms and Baron lives, you can end up with NINE yetis total (!!!). Doubt that happens often, so let's look at Cairne dieing on turn played. Even if Cairne dies and becomes Baine before you get to pull it off, you still end up with Cairne that was killed, then Baine that you trade/suicide into becoming 2x Baine, so still four Yetis for three cards, plus the 1/7 that needs to be dealt with for fear of any other Deathrattlers you might play.
I just think the potential for Ancestral Spirit and Baron is massive for Shamans, regardless of what you use it in conjunction with because from turn 6+, any minion you have left on the board can become a suicide removal that respawns two fresh copies of the same minion, WHILE giving you what could be considered a high threat 1/7 legendary to deal with. Any other obvious Deathrattles are bonuses - but Shamans have a card that add a dangerous deathrattle to anything, much better than Druid's Soul of the Forest to spawn an army of 2/2s (although that will be a new take on the savage roar druids).
Edited by Ranilin on 4/11/2014 1:30 PM PDT