Advance with Caution:
Make sure you end every turn with your solidiers in cover and when you do come out out of concealment avoid running ahead as this could trigger an enemy encounter halfway through a turn when you are not prepared.
Easy 'Now Am I Become Death' Achievement:
You will be able to get this Achievement easily if you use the 'Faceoff' Sharpshooter ability and shoot your pistol at at leaset 3 visible targets that are within range, this also includes those that are wounded.
Unlock Characters:
In Single-Player Campaign go to the soldier's customisation menu and select 'Character Info', then enter the following names (without the quotes) to unlock the corrsponding character. Note: Entering these codes will disable Achievements.
Beaglerush (Grenadier)
Enter 'Beaglerush (nickname)'
Peter Van Hoorn (Assault Build Ranger Colonel):
Enter 'Peter Van Hoorn'
Sid Meier (Psi Operative Magnus):
Enter 'Sid Meier'
Cheat Mode:
The following requires editing a game file so it is advised that you create a copy before proceeding. Find the '(x86)SteamsteamappscommonXCOM 2XComGameConfig' directory and using a text editor edit the indicated files to the following to get the corresponding effect.
Increase Squad Size:
Change 'DefaultGameData.ini' to 'MaxSoldiersOnMission'
Fewer Enemies in a Mission:
Change 'DefaultMissions.ini' to 'MaxSpawnCount'
Low HP Enemies:
Change 'DefaultGameData_CharacterStats.ini' to 'CharacterBaseStats(eStat_HP)'
Powerful Weapon Attachments:
Change 'DefaultGameCore.ini' to 'FREE_KILL_BSC' or 'FREE_RELOADS_BSC'
Specialist Shotguns:
Change 'DefaultClassData.ini' to 'AllowedWeapons=(SlotType=eInvSlot_PrimaryWeapon, WeaponType='rifle')'
Magnetic Rifle Damage:
Change 'DefaultGameData_WeaponData.ini' to 'AssaultRifle_Magnetic_BaseDamage'
Grenade Explosion Radius:
Change 'DefaultGameData_WeaponData.ini' to 'FragGrenade_Radius'
Clothes and Beard:
Change 'DefaultNameList.ini' to 'NewSoldier_HatChance'
Movement Speed while Carrying:
Change 'DefaultGameCore.ini' to 'CARRY_UNIT_MOBILITY_ADJUST'
Better Shadowstrike:
Change 'DefaultGameData_SoldierSkills.ini' to 'SHADOWSTRIKE_CRIT'
Better Conceal:
Change 'DefaultGameData_SoldierSkills.ini' to 'STEALTH_CHARGES'
Resistance Contacts:
Always try to establish resistance contacts as doing so will enable you to gain extra funds and region-specific upgrades which will come in useful if Alien Facility missions spawn in those regions.
Squad Members:
A good tactic when selecting six squad members is to take a representative from each of the five available classes. Doing this will give you a better chance of dealing with any unexpected circumstances as there will be more skills in your team.
Avatar Project Delays:
Try to delay completing the Avatar project for as long as you can so you give yourself more time to research tech and unlock stuff making you better prepared for when it is completed. You can delay things by taking on Guerrilla Ops assignments and when the bar reaches it's halfway point, complete Alien Facility missions to drop it by at least two points.
Rewards:
When you are given the opportunity to select the rewards you recieve always go for Engineers, Scientists, or Intel as they will be the most beneficial to your campaign. Engineers and Scientists allow you to upgrade your troops and base more quickly and Intel will help you establish links with new regions.
Advanced Warfare Chamber:
The Advanced Warfare Chamber is a good choice when selecting a facilty as it offers a host of benefits such as halving the time you have to wait for soldiers to heal and additional skills when they level up (from other character classes).
Ranger:
A good strategy when you come out of concealment is to keep the Ranger at the front of the group and make the others follow a square or two behind.
Mercenary:
The best strategy is to adopt a mercenary attitude and focus your attention on the nations who give you the most money each month.