WQell Verdian, you (and quite a few others) should love the next update. My main change is going to be to the dangerous features. Primarily they will have a limit to how many creatures they can spawn at once, and how many they can spawn throughout the game.
My ideal is to create unique units for almost every feature, but till then I am looking to stick with summoned units as much as possible (so Letum Frigus and the Maelstrom will change).
Looks like I may have forgotten to give the lions a workrate

I tried to make sure to set it to 1 turn for building the dens on each beast, so I'll get that fixed probably (wierd thing is that lions can cast a spell to create a den, "Release to the Wild" which I don't remember ever seeing before. Maybe that was lion prides...)
Never is used in general to forbid access to various things which are used to make the game work. Promotions are linked to it so you cannot buy them via level-ups. I THINK that the same would be accomplished by just leaving the available unitcombats blank, but this way is one which works for certain
Yes, most likely the animals jumping across the map was due to a barbarian version trying to spawn instantly. Fortunately only Barbarian can normally build dens so it isn't an actual issue (I hope).
By way of Preview, the future plans for the Unique Features:
Maelstrom: Spawns The Sailor's Dirge. Will continue to spawn him anytime that he dies, so he will terrorize the waters all game.
Pool of Tears: Spawns Echoes of Sorrow, which will sap the will out of anyone who comes too close.
Letum Frigus: Spawns up to 4 Frozen Souls at a time.
Tomb of Sucellus: Spawns 1 Wandering Alchemist at a time
Dragon Bones: Spawns 3 Desert Cobra at a time.
And the rest will have various limits placed on the current spawns for how many they can have at once and over the course of the game. So you will still have to clean them off occasionally through the early game, but by endgame they stop spawning eventually.