FormerlyHemlock
Hero
I'd like to hear how others might have run the battle or the PCS. I'll leave a little time to talk before discussing travel and starting encounter 2.
Encounter 2 will be much tougher and require more resources. The terrain advantages and abilities of Death Slaad will tax the party heavily. AoE damage dealers almost always tax a party more than single target damage dealers.
Given the crowded conditions, I would have approached the battle slightly differently: send a bunch of (Inspiring Leader-enhanced) summoned Giant Owls through the Teleportation circle first with orders to spread out throughout the whole room while readying a Grapple against any creature which approached them, followed by PCs. In fact, sending ahead a scout followed by immediate dispersal should be standard operating procedure for any travel through a chokepoint like a teleportation portal or dimensional vortex. Sixteen 10'x10' giant owls in a checkboard pattern (with 37 HP each) should clog the space enough that the giants can't get through, nor the wolves. Then you just kill the giants with ranged attacks, or more hopefully, negotiate their exit without violence when they see how outmatched they are. If it comes to a fight, you may lose a few owls or a few HP, but to a first approximation the only resources you're spending on this encounter are (1) 5th level slot to cast Teleportation Circle, (2) 5th level slot to cast Conjure Animals, (3) Thirty minutes of exhortation time, (4) a bunch of arrows.
This SOP of immediate dispersal will help against the Death Slaads too.
I gather there's enough travel time that you won't still have the original batch of owls available any more (2 hours travel time, I hear? Can't see the original post) so it'll cost you another spell slot to get more meat shields, which is too bad, but it's still pretty cheap. (If you knew in advance that there were only going to be a bunch of Frost Giants in the first encounter you probably would only cast Conjure Animals III, since V is overkill, but you don't know that so you'd blow a 5th level slot in both cases.)
Even if the Death Slaads get super lucky and hit four PCs with 60 HP of fire damage each (poor dispersal plus good initiative plus failed save plus good damage rolls plus no Counterspell from PCs) that's still only 240 HP of damage, which is equivalent to a single Extended Aura of Vitality from your healer if you optimized healing. And besides, only 42 HP per PC is real HP damage, since each PC has 18 temp HP.
Conclusion: if your DM likes to "start the encounter" with the party in poor tactical position (clumped for AoE), the Death Slaads will be annoying, but still not that expensive to deal with.