After the update, first enemies that most people face is the zombie excluding some areas that they meet other creatures, slowly and steadily skeletons join the zombies ranks, they are just moving bones that are weak against smashing (for an example the starting weapon rod work perfectly well against them) as they are almost resistant to slashing and bullets as bullets have more chances to pass through them even if bullets break a few of their bones same as for slashing or stabbing, they can still move but the humans always have ways to counter them like smash them using the butt of the rifle or use a hammer, maybe because skeleton are weaker than zombies or they are simply a pile of bones, they have much lower experience and drop rates than normal zombies but their numbers surely make up for this so called lack of loots for survivors

Undead are very patience on their attacks, through their constant siege in the combination of constant horde attacks, those are following threat that could be most annoying or life threatening in SLS.

1st on the list is the skeleton which first appears on the 3rd day after the update, as the military tried to contain by them through firing of the guns but it end up exhausting their troop strength and forcing them to save ammunition against whatever skeletons threats, as they have spawn against the zombie ratio 3 is to 1 plus they have 2 of the most annoying skill that is so called "dodge the bullets"  as some bullets fly through their bones or block vision or accident block the bullets as they charge to the survivors with rusted weapons. A group of calm survivor fights them on front melee will wipe them instantly, those who choose to over depend on their guns or they overextend their area through spreading their defense line will find out that they exhaust their ammunition for expedition or defense than are wiped out due to lack of ammunition and medical supplies due to their overwhelming numbers.

2nd right after the list is Ghoul which is one of special zombie that appear on the 6th day. They consume other dead flesh to strengthen themselves, its teeth and fangs are covered in extreme poison or virus that will cause the one to turn another ghoul if affected. It is easy to identify ghoul from normal zombies as they smell worse than normal zombies and they are more like cowards in the battle so finding them running away is pretty common as a result they are one of the hardest to kill in the list.

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They have high attack power, good at tracking, best in ambushes and also surprise attacks making the survivors hard to expand their borders as if there is a leftover survivor, they will quickly ambush that survivors, aim to kill or scratch their victims as it maybe increase their numbers if the wounds are not treated properly.

Normally a battle will always lead to another battle due to their tracking skill which eventually weakens the survivors if they choose to keep fighting and not to find a spot to reduce their blind spot. Having the safe spot that your allies can cover you can temporary allow you to rest but you will never escape their hunt as they will keep hunting you down to your team get to wipe out or you manage to kill them.

3rd is other survivors yeah you hear it correctly humans, morally humans will be less dangerous than other threats but now mankind themselves because of a bigger threat to themselves than other threats, humans will hunt another for easy EXP and you guys know survivor pack, even their meat can be eaten without much treatment. Plus free starting weapons from looting their bodies, what you do not like the starting weapons, just fuse it with the leftover bodies to improve your current weapon. The best part is no downsides at all, if the user of the weapon died another will pick up and use it to it almost break down then fuse it with other weapon or etc to repair it and the cycle repeats again and again in order to make the weapon stronger and more efficient. Like the man-eating tribe, this is man eating terrible in real life wearing powerful clothes and weapons basically mini bosses, some of them are same from the past with the system update they mass restart on their lifestyle, some is lazy or too scared to die so they begin to do this, most of them do blood ritual and etc and grant some gods of protection which make them even stronger and powerful ....