Okay, for cheering, etc, do you have Stony Beach yet? Because downloading that includes a number of universal one-shots that have the majority of those great reactions (gasp, groan, applause, etc). Then use the Theater set from Dragon’s Heist, which has a number of audience sounds (nice audience, rowdy audience, laughter, etc). There’s also an element called “halfling play” which is wordless sounds that could sound rather insulting indeed for a heckler!
For the toxic plant spores, try the Corpse Lotus Battle, perhaps combined with the Vrock Battle (as that also has a spore release one-shot).
Cockatrice - have to combine some here. Use Descent into Avernus - Path of Demons Part 1 - and use the “abyssal chicken” element. Combine that with some of the “Flying Fiend Battle” for hisses and wingbeats, and then use the “ice spell” universal one-shot for its petrification bite.
Bear - Dungeon of the Mad Mage 7 has a great “cave bear battle” mood. Or Tiger Battle can suit as well.
Vipers - use the “giant constrictor snake fight” in Wild Beyond the Witchlight 2, the Locations in Hither set, and then add in from Flying Fiend Battle the “flying fiend hisses” and “flying fiend bites”, which sound like really sharp bites.
Water Mephits - the “mud mephit fight” from Wild Beyond the Witchlight 2, Arrival and Random Encounters works pretty well, you’d just have to add some additional water elements (from Elements - Rain or Down Comes Rain, perhapts).
Crazy Druid with Swarm of Rats - “crazy laugh” from Dragon’s Demand - Dragon Slayers. D&D Druid Spells. And Curse of Strahd’s Village of Barovia I - “rat fight” (which is a swarm).
I hope that helps!