Hey there!

Mutons are dangerous in close proximity. While I don't know for sure if they get +10% Aim bonus from melee attacks like some units, for example, Stun Lancers and Archons (I have no complete list of the units with and without this Aim bonus for melee attacks), they are very damaging - up to 11 damage. However, IIRC, they can't run just like Lancers or Rangers and attack at the end of their dashing movement. Nevertheless, they are claimed to deal a finishing hit to stunned units (again, can it be dodged or do soldiers have chances to bleed out instead of being insta-killed?).

Their beam rifle is very damaging as well - up to 8 hitpoints with a crit damage (and they have at least 10% crit, even if they shoot at a unit in cover; vs flanked unit the crit gains +33% or +40%, depending on the game difficulty).

If you group at least 2 of your units close to each other, then a Muton will throw a plasma grenade (I suppose that its blast radius is the same as for grenade launcher frag/plasma grenade - this needs testing/verifying). It is the least damaging weapon (4-5) and should have only 1 charge. However, if the blast destroys elevated surface the units are standing on, they will also take fall damage (depending on how high they were positioned, usually averaging from 2 to 4 damage). Additionally, destroying the cover of your units allows the enemy to set up high crit chance attacks without aim penalty. So if a Muton acts first in the enemy pod and starts with a grenade throw, the following attacks might be devastating for the targeted player units.

To sum up, a Muton's fairly high (for an enemy unit) 80% Aim, somewhat high (up to 11) HP pool and armor (up to 2), inherent 10% Defense (i.e. a unit targeting a Muton will have -10% Aim penalty due to this stat), for an early game enemy on Legend difficulty it poses high risk and must be eliminated as a priority target.

And once again, if you are not able to neutralize a Muton outright, either consider backing off (if circumstances would be more favorable to you) while keeping every unit in cover, unless baiting with a unit to be hit while supporting it with Aid Protocol / Smoke cloud / Hunker down. Or temporary limit a Muton's abilities and Aim with Flashbang. On a side note, a Muton can use Suppression Fire instead of making a regular shot (the triggers for this ability are in the game files, but, probably, a high cover (+40% Defense, i.e. -40% Aim for hostiles) could be one of the causes). Fire burning should also limit all his abilities to just a regular shot, which is high damaging nonetheless. Poisoning with Venom rounds reduces Aim and Movement.

So, unlike a Stun Lancer, who gets severely debilitated by a Flashbang and, to some extent, with fire burning (it doesn't lower Aim and enemy units can't Hunker Down to "waste" their action points), a Muton and a Heavy Lancer are able to deal up to 8 hitpoints of damage with their primary rifles. If there is no elevation to take advantage of for the height aim bonus, a Ranger might need to approach very close to negate the Muton Defense stat (XCOM ranged weapons get high aim bonuses for being close to an enemy, excluding a Sniper Rifle, which gets penalty); a basic shotgun can deal up to 9 damage with a crit hit. A Grenadier can setup a possible follow up kill by a Ranger by softening up or removing armor and reducing a Muton's HP with a grenade or a lucky cannon shot with Shredding and, likely, Holo Targeting. A Sharpshooter is highly accurate as a pistol Gunslinger up close, though not very damaging, and a Specialist is guaranteed to deal damage with his Combat Protocol (albeit, Medical Protocol ability is far more valuable to choose it over Combat Protocol, in my opinion, especially if going for no casualty campaign runs). A Psi Operative should be very powerful mentally vs Mutons, who have a really low Will stat of merely 50 points.

P.S. I have mostly (and somewhat recently) played on Legend difficulty (and WotC), but started with Veteran (base game). Mostly due to game difficulty differences: lowered Research speed (i.e. no fast-paced weapon/armor upgrades), no quick Autopsy instant completion (more corpses are required), higher stats for enemy units (primarily HP, but also armor, etc), and higher cost for (almost) everything - my "advice" doesn't include tier 2 weapons and armor, nor often use of experimental grenades and ammo (which usually require 2x time to research in the Proving Ground), nor weapon mods or PCS (some of which can be very impactful), nor lucky continental or scanning bonuses or Black Market assortment.

Thanks! Also, any tips on snakes?? They’re sooo annoying and I’m hoping to get a Hellweave vest soon but is there anything I can do until then? (I need to beat a chrysallid first and I haven’t encountered one yet)

Yeah, the Vipers can be annoying and can pose high threat to separated soldiers, if they Bind&Crush. If they poison a unit, he or she can die if the poison persists for too many turns (e.g. up to 5), though it is only -1 HP every turn.

As usual, fire and Flashbangs debilitate them severely in terms of offense. They have 75% Aim, so a high cover (+40 Defense) and disoriented debuff (-20 Aim) would make it merely 15%. Fire prevents any abilities, except for using the primary rifle, but doesn't reduce accuracy.

If you group 2+ units, the Viper will most likely Spit Poison instead of other attacks (if not disabled by fire or disorientation), however, it could go for a flanking shot. Besides, the Tongue Pull cannot be performed every turn (it is stated to have 2 turn cooldown). Equipping any kind of medikit makes a unit immune to poison, but the game doesn't cheat in this aspect and a Viper will not know (i.e. will disregard) this and would still spit poison. An older entry on the Wiki claimed that a Viper Poison Spit does flat damage on impact (some game files claim the same - apparently, the added info was sourced from the game files just like most info added to the infobox at some point then), but that is opposite to what is in the actual game - there is no impact/blast damage.

Hellweave vest will only activate after a unit wearing it is attacked in melee (I didn't test it vs Viper Tongue Pull), but not prior to it. So, it will most likely harm more than help, if a unit would be pulled and then released due to vest damaging the Viper - the unit will be exposed to flanking enemy shots on the same turn of the enemy (the Viper, or one of them in a pod, might be the first one to act on the enemy turn phase). [however, if it somehow interrupts the Tongue Pull, then it is useful, at least in this aspect]

Viper's dodge can be annoying as well: the damage gets halved due to Dodge and is also rounded down (up to a minimum of 1). E.g. a 3 damage shot would result in 1 damage only if the Dodge triggers (it can trigger at accuracy below 100%). However, a Stock weapon mod can be very helpful in releasing a pulled and bounded unit - even if a shot misses, the damage will be applied to the Viper, which will force it to release a unit.

Again, softening up a healthy Viper (e.g. with a grenade) and finishing it up by Ranger works well. Not a high threat unit in my book, but can deal a lot of harm, if not prepared for an unexpected encounter (i.e. in undesired circumstances, like being already engaged with strong pod).

It doesn't have Defense stat, so it is not as difficult to hit as a Muton (or anything else with Defense). Also, this enemy doesn't scale with the game progression, so it will soon fall off as a weak being by itself.

But the Viper potentially poses danger to units due to its inherent crit chance (10%) and the maximum damage with crit of up to 7. Supporting a somewhat exposed unit with Aid Protocol and/or hunkering down can save a soldier. It is generally better to have a Flashbang rather than a Smoke Grenade, though the latter can be used to cover the whole group and is more effective the less accuracy an enemy has (due to disorientation/poison/aim penalties for targeting units in cover).

Btw, what difficulty are you playing, what is the current date in-game, and are tier 2 weapons and armor research complete?