MarkB
Legend
So all your monsters have a separate init? I think you over stating the case. The is a boss fight with waves. First wave is 4 or 5 guards. Depending on how you did earlier. The boss is protected by box text. Once the first wave is killed, the second wave comes.
Second wave is 8 blood hawks which will operate in teams of two using pack tactics. So in this case one pc is not a target. The villain is escaping but can be engaged by missile weapons. If both blood hawks hit, the avg damage will zero a wizard. The hippogriff is also present. But the group can grab the prisoner and retreat.
I can see this being a tpk if the dm is not careful. Especially if everyone is first level. While I don't train my monsters to SAS team tactics, I will use their abilities. I have dm this mission at least six times. How I run depends on the players and levels of pcs.
The only issue I'd have with this scenario is that it effectively requires the monsters to "know" that they're acting on a group initiative, and that if they move and ready their actions they'll still all get to go before any of the PCs get to act. If the situation were reversed, this would be an extremely risky move - if the first PC to act ran off ahead of the rest, he'd have no way of knowing whether his allies would have the opportunity to immediately charge in after him, or if he'd suddenly find himself alone and outnumbered as multiple opponents took their turns, holding a readied action that he might not survive long enough to trigger.