You Win, Everything
Awarded for gaining all other trophies.
Who Needs Limbs?
Augment a soldier in single player
Early in the game you will be given the option to build a Cybernetics Lab. Once this is achieved it can be accessed through Engineering, you can then choose a soldier to be turned into a MEC which requires the removal of limbs. When this is complete access this soldier through the Barracks, ammend his loadout to put him in a MEC suit to achieve this trophy. There is also an initial outlay of $10 and 10 meld.
A Little Bit Alien
Modify a soldier in single player
Early in the game you will be given the option to build a Genetics Lab. Once this is complete access it through Research, choose a soldier to have their gene or genes modified. This soldier will be removed from action for 3 days per upgrade, once they return to action this trophy will be achieved.
Get a Soldier to have 5 modifications in single player
There are 10 available gene mods, five must be equipped to earn this trophy. There are two for each of brain, eyes, chest, skin and legs however only one can be applied from each pair. They can be swapped out at a later date but any meld spent is not returned. They can be accessed through the Genetics Lab and each will take 3 days to apply. Here is a brief description of each one. I will flag anything specifically needed for a trophy.
costs $35 & 10 meld, unlocked by Sectoid Commander autopsy, causes damage to psi attackers, needed for Mental Minefield.
costs $35 & 20 meld, unlocked by Beserker autopsy, grants a will boost when defending a psionic attack.
Hyper Reactive Pupils
costs $15 & 5 meld, unlocked by Meld Recombination research, +10 aim bonus after a miss.
costs $15 & 5 meld, unlocked by Meld Recombination research, +5 aim +5 critical chance for height advantage.
costs $25 and 10 meld, unlocked by Muton autopsy, grants boost to aim, mobility & critical to nearby soldiers with a kill, needed for Anger Management.
costs $75 and 15 meld, unlocked by Cyberdisc autopsy, soldier will be critically wounded instead of dying when HP reaches 0.
costs $35 and 15 meld, unlocked by Chryssalid autopsy, causes unseen enemies within a short distance to be revealed, needed for Tingling Sensation
costs $75 and 35 meld, unlocked by Seeker autopsy, soldier becomes invisible but with severe restrictions.
Muscle Fiber Density
costs $60 and 25 meld, unlocked by Thin Man autopsy, enables soldier to reach high positions, needed for Mind The Step
Adaptive Bone Marrow
costs $30 and 15 meld, unlocked by Meld Recombination research, reduces wound recovery time by 66%.
Deploy three tactical subsystems on a single soldier in single player
Unlocking all three upgrades on a MEC will cost a total of 200 meld and $176. The final upgrade isn't available until after Titan Armour research. The final upgrade costs 100 meld, if you think that meld could be better spent elsewhere save immediately before applying this upgrade then return to this save after achieving the trophy.
Deal with the newest global threat
This will be awarded for successfully assaulting the EXALT base. Your special agent will return from his undercover missions with information about the location of the EXALT base, use this information to guess its location. A correct guess leads to the base assualt, an incorrect guess leads to that country leaving the council. If you wish to speed up this process save, spam guess until you reveal its location, load save and guess correctly. I don't recommend this though as it makes Where in the world
impossible to obtain.
They Shall Not Pass
Eliminate all alien waves
This is story related and cant be missed. Aliens will invade your base, kill them all. Be sure to get all hands on deck
at this time.
Eradicate the infestation
Early in the game you will be asked to complete a Council mission set in Newfoundland, accept and complete this mission to achieve this trophy.
An Army of Four
Beat the game without buying a Squad Size upgrade on Classic or Impossible difficulty
Toughest trophy in the game. Start a new game, choose Classic difficulty and do not increase your squad size through the Officer Training School. Clever use of game saves is the only way to achieve this, make sure Autosave is off so you are in full control of your own saves. Create 3-4 save files and cycle through them, if you do something well save, if you do something badly return to your previous save, if you trigger enemies and are unprepared load a previous save and remember the spawn point. Prioritize laser/plasma research, get rapid recovery as early as possible, build a MEC or two to inflict some heavy damage, launch as many satellites as possible and always keep a couple in reserve, use the grey market to generate funds if need be. Stall the Alien Base Assault until you are comfortable with your available armour and weapons. I recommend starting in Africa for the extra funding. As you only have 4 soldiers per mission the promotions will come quicker, choose your upgrades wisely. Overwatch is no longer your friend, hunker down is a better option, it's better to give the enemy no shot than a shot you can react (badly) to. I would wish you luck, but luck has nothing to do with it, it's all about the saves.
Here is some advice from zz383
The Meld Squad
Field a fully enhanced squad and win the mission
This is achievable with MEC's, gene modified soldiers or any combination of the two.
Eliminate an enemy's shield and kill it on the same turn in single player
This is a Mechtoid, a Sectoid in a a MEC suit. A nearby Sectoid will preform a Mind Merge with a Mechtoid to give it a shield worth an extra 6 HP on top of its own 20, it also reduces damage done to the Mechtoid by half as long as the shield is up. You will need to destroy this shield and the Mechtoid in one turn to achieve this trophy.
Someone Your Own Size
Kill a Muton Berserker in melee combat in single player
To achieve this you will need a MEC with Kinetic Strike Module equipped, a 12 HP melee attack which can be upgraded to 18 through The Foundry. The Beserker is a melee only Muton, he is quite aggressive and will run towards a soldier who has successfully landed an attack sometimes causing him to panic and miss a turn. Use this to your advantage, draw him into your designated MEC then move in for the kill.
Taking A Load Off
Stop a squad member from suffocating in single player
The Seeker is a flying squid like alien that will go into stealth mode as soon as it is triggered, they usually travel in groups of two. After they enter stealth mode they can appear at any time to suffocate your soldiers, so don't leave any isolated. Be sure not to enter Overwatch until you have achieved this trophy or you will kill the Seeker before they have a chance to suffocate your soldiers. They will not try to suffocate your MEC.
Where in the World
Make certain of the new threat's location
The trophy description is here slightly misleading as you must make sure of the EXALT base by carrying out infiltration missions, not simply by making incorrect guesses. There must be an X beside each countries name in the Covert Operations menu except the country harbouring the EXALT base. Put simply you must carry out all available covert missions to achieve this trophy.
Mind the Step
Jump two stories in one move in single player
Carrying out a Thin Man autopsy gives access to Muscle Fiber Density, apply this to one of your soldiers and they will be able to leap 2 stories.
Use Collateral Damage to blow up a car in single player
Use a MEC's Collateral Damage ability to target and destroy a car to achieve this trophy. A kill is not required but is always helpful. All Mec's have this as a strarting ability.
By Our Powers Combined
Field a squad with 4 augmented soldiers, each with a different base ability and win the mission
Turn a support, assault, heavy and sniper into MEC's, take these four into a mission and win to achieve this trophy. This will also unlock The Meld Squad
and Rise of the Machines
if you haven't already.
Rise of the Machines
Field a squad consisting entirely of augmented soldiers and SHIVs (min. 4) and win the mission
This is achievable with a fully MEC squad, the Shiv is optional. Leave out the Shiv and you will also achieve The meld squad
Field a squad where all members have at least two modifications (min. 4) and win the mission
Apply 2 gene mods to at least four soldiers, win a mission with these four soldiers to achieve this trophy.
Kill an enemy as it is psionically attacking you in single player
Equip a soldier with Neural Feedback, isolate and soften up a Sectoid Commander and put him in a position where he can only attack this designated soldier. His psi attack will be repelled and 6-7 damage will be inflicted, causing him to die. This approach will also work on an Etheral but they have a much higher HP.
Proc Combat Rush on the entire squad (min. 4)
Carry out a Muton autopsy to unlock the Adrenal Neurosympathy gene modification. Apply this new gene mod to a soldier and he/she will 'combat rush' all nearby soldiers when completing a kill. It's range is quite large but try to keep it tight until you achieve this trophy.
Remington... Max Remington
Have your special-duty soldier kill three enemies in the same mission
These are EXALT operatives, you must kill 3 of these with your special duty soldier during one extraction mission to unlock this trophy. He/she will only be equipped with a pistol and whatever you may have in their inventory slot, they will also maintain whatever abilities you have allotted within their class. Improved pistol 1,2 & 3, equipping laser/plasma pistol & using a sniper with +2 pistol damage will all give an advantage.
Kill an elite enemy Sniper with one of your own snipers in single player
This can be achieved while on an extraction mission. While aiming at an EXALT agent press L3, this will highlight his class. When you find an Elite Sniper kill him with your own sniper to achieve this trophy.
Kill an elite enemy Medic with explosive damage in single player
Similar to the above trophy this should be achieved on an extraction mission. While aiming at an Exalt agent press L3 to highlight his class. If you find an Elite medic kill him with explosive damage. Make sure to equip some grenades before going on extraction missions until this trophy is achieved.
Kill an unseen enemy detected by a specially modified soldier in single player
You will need to apply Bioelectric Skin to achieve this trophy. This will cause untriggered but nearby aliens to appear as a shimmering kaleidoscopic oval shape. As they can't be seen they can't be aimed at, rocket launchers and grenades are the way to go.
Pain in the Neck
Cause an enemy to suicide
To achieve this trophy you must use an Arc Thrower on an Exalt operative. Soften him up with gunfire to get his HP to 3 or lower for the Arc Thrower to be most effective.
You will be offered a council mission on a damn in eastern France, accept and complete this mission to unlock this trophy. I wasn't offered this mission until after I shot down the Overseer.
Ours are the Furies
You will be offered a council mission near the alps, accept and complete this mission to unlock this trophy. All people rescued on this mission will have latent psi-abilities and will be added to your squad.
Beat a new special mission without losing any assets
Here is a screenshot of the mission where this trophy can be achieved. Do not allow the yellow 2 in the top right hand corner turn to 0, this may seem vague but it will make sense as you play the mission.
Guardian of Earth
Designate a highly decorated soldier as the Volunteer
There are five available medals, the figure in brackets is the maximum amount of each medal you can earn
Urban Combat Badge (4) awarded for completing an urban map mission
Defenders Medal (3) awarded for a soldier dying, being critically injured, stabilized or gravely injured during a mission ( a soldier must die to get first)
International Service Cross (2) awarded for completing a mission outside you base continent
Council Medal of Honour (2) awarded for completing a council mission
Star of Tera (1) awarded for completing XCOM Base Defence
When you have discovered a soldier with psi-abilities, put him/her in psi armour, upon entering the Gollop Chamber this soldier will be The Volunteer.
Award him one of each medal to achieve this trophy.
All Hands On Deck
Get at least 4 kills with XCOM Base Security personnel
During the second half of the game your base will be invaded by alien forces. During this attack you will have use of 6 of your own soldiers and 5 base personnel. You will be attacked by waves of enemies (i achieved 34 kills in total). Kill any 4 of these invaders using base personnel to unlock this trophy. They are equipped only with one grenade and a starting rifle so enemies will need to be softened up first.