I am using Big Monsters in my current game. The settings and mods are for an extreme marathon game. More expensive than marathon, with some railworld and deathworld settings. As such, I am over six hours into the game, but I barely have military tech going and am just into seeing some big biters from normal spawns (Evolution is about 0.6).

So far I have gotten a few groups of enemy soldiers and biters from your mod that I have dealt with without any real issue, but then disaster struck and spitterzilla appeared. 180k HP, only 28% resistance to all but explosives, but it would take about 2000 AP magazines to bring it down at my current tech level, assuming the turrets aren't destroyed before they spend all the ammo. And I don't have much else to work with, a few companion drones (Klonan mod), and grenades (way too slow). With the enemy range (72) I would have to manually go in and place the turrets, in an area heavily coated with acid splashes where a single direct hit would one-shot me. Not that I have enough bullets, without stripping all my defenses. This mod is serious business, I expect to have to dump enemy HP in mod settings if I am to kill it.

But how is enemy strength scaled, description says it is scaled based on number of players and evolution, but in my extreme settings that seems insufficient.

evolution is the base thing here. Your 0.6 evo seens too high for your current tech level (that is normal for a deathworld setting). So you might want to adjust some settings here to fit your play. On todays version, I've added options to set the minimal evolution for all events.

Yeah, it's an extreme marathon game, on top of normal marathon I doubled cost of all basic intermediaries, such as plates, bricks, plastic, etc and halved energy value of wood and coal. I also have a research multiplier of 6x. So all research costs 3x marathon settings in terms of basic resources. AP magazines cost 10 copper ore and 28 iron ore each, or a total of 76000 ore minimum to deal with that one giant spitter boss. Actually even more because of Swarmageddon mod causing it to split into even more enemies. Pretty brutal like that and I had actually processed nearly 1M iron ore at that point. I think my evolution/pollution settings are equal to the standard Deathword Marathon setting, which is not as extreme as normal death world, but still far worse than just default. And in terms of evoution to tech level, far worse than normal deathworld.

Still I decided to remove the mod. While I liked it and it is interesting, it was not really what I wanted for this playthrough and I got tired of dropping everything to deal with whatever threat it threw me since the automated defenses were useless, at least with only gun turrets. And distances were far too large since I didn't even have a car yet. But this new minimal evolution setting might make it worthwhile, that can delay the more dangerous events until I got the technology to deal with them. I might check it out again.