THIS IS NOT A GENERAL SPY TACTICS TUTORIAL, IT IS ALSO A LONG READ!
'Bring your Dead Ringer up' right click and your Spy will bring his watch onto the screen, I say this as 'activating' it isn't really true as to activate it you need to take damage
"Feign death" When your Dead Ringer is activated it will leave a false body and re-enact what would really happen if you died.
"Sap & Stab" Useful Tactic where you sap an Engineers building and he comes over to repair it when you are lurking behind him and back stab him before he gets rid of the sapper
"Stab & Sap" Another useful tactic where you quickly back stab an engineer near his buildings and quickly sap his Turret before it kills you.
2) What is a Dead Ringer?
The Dead Ringer is a cloaking watch for the Spy which feigns your death; it deludes people into believing they have killed you when they have only triggered the watch.
First off, you will need a Dead Ringer, this can be acquired by getting the Spy Achievement Milestone 3 or bought for a scrap off traders or bought with real money for $0.99 or £0.59 (not advised)
3) Revolver choices
For your revolver I suggest the L'Entranger as you get 15% cloak every hit but does 20% less damage (yet who cares?) or an Enforcer as 20% extra damage but takes longer to fully to cloak (Dead Ringer is unaffected) and decloak (Dead Ringer is affected)
4) Knife Choices
A good knife to use is the Big Earner as upon a back stab you will regain 30% of your cloak which can be extremely useful however it lowers your maximum health to 125, 25HP less than usual. Another good knife to use is the Spy-cicle as when you are ignited by a Pyro then instead of you setting on fire it will melt the knife and leave the Pyro believing he killed you as you just feigned your death.
Some useful tactics to know are Sap & Stab or Stab & Sap and general knowledge of how to play as a Spy
5) Dead Ringer Pros
-Feigns your death and cons most people into believing they killed you
-Regenerates 60% faster
-Decreases the amount of damage taken by 90% (making you invincible to back stabs and head shots)
-Can be used indefinably when stood next to a level 3 dispenser
6) Dead Ringer Cons
-Cannot cloak at will, only when damage is received
-Makes a very distinctive and loud sound when you decloak (unless you have the Saharan Spy set (talk about that later)
-Resets to 40% cloak if you decloak over that but leaves it if you are under 40%
-Ammo boxes restore less cloak than the original watch
-Doesn't feign everything
-When your death is feigned, it will give the enemies certain achievements D: (e.g. Shoot the breeze)
-Only lasts 6.5 seconds
7) What Dead Ringer doesn't feign
When you die, certain weapons have a kill effect the Dead Ringer will not re-enact these weapons when you feign your death: Candy Cane, Killing Gloves of Boxing, Holy Mackerel and Unarmed Combat, Powerjack, Your Eternal Reward, Half-Zatiochi, Conniver's Kunai, Spy-cicle, Machina double kill
Sentry Gun kill and assist counts
8) Starting Off
A good way to start off is immediately as you spawn is to bring up your disguise kit and disguise as your own team, this way the enemy team will not think much of you using a Dead Ringer when you look like a Demoman.
After, select your sapper while disguised as your friendly Demoman and press your last disguise button (default B), this will make you appear to have your Demoman's secondary weapon out. I tell you this as many people do not seem to know. If the Demoman you're disguised as has a Splendid Screen or Charge 'n' Targe then select your primary weapon instead.
Now with pull up your Dead Ringer, this is very good when advancing to the front lines as you may get hit from an unexpected angle and waiting to respawn is a pain, so after you get up to the enemy lines you will no doubt be hit by something or other, people will not get suspicious as if you are near any of your team mates they will be focusing on killing your team instead of 'WOW! I one hit that Demoman!' as if they do your team will kill them and you won't have to worry about them anyway. Once your Dead Ringer has been activated you should then disguise to the enemy team and again, select your sapper or knife and press the last disguise button to appear to be holding that persons secondary or tertiary (third) weapon.
Now you can move about freely in the enemy team's base and try to avoid confrontation while your Dead Ringer recharges as it is useless not at 100%, the Dead Ringer does recharge if you pick up ammo packs so pick them up if you can.
Now when your dead Ringer is full bring it up again encase you stumble upon a Soldier who decides he will waste some ammo on a ‘friendly’
9) Killing Engineers
Now you're successfully deep within the enemy’s base and you have found an Engineer a good tactic is to be glaringly obvious that you are a spy and run up, pull down your Dead Ringer and sap his stuff and bring your Dead Ringer up again. He will naturally remove the sappers and shoot you in the face with his Shotgun, once he has triggered your Dead Ringer and get out of there, re disguise, pick up some metal and run back in there, the Engineer will be relaxed as he thinks he has fended off a stupid Spy attack, now Stab & Sap or Sap & Stab (if you don't know what these are I told you this is not a general Spy tactics tutorial) and he will not be bothering your team for a while.
10) Killing everyone else
Playing as a Spy with the Dead Ringer varies massively to a Spy with the Cloak and Dagger but killing people is generically the same, run around disguised as the enemy team with your Dead Ringer up and pull it down before backstabbing enemies.
11) What do I do when being attacked by a Pyro?
Now if you have been spy checked by a Pyro while your Dead Ringer was up chances are that they have activated it and continued burning you and lighting you up while cloaked. You should leave your Dead Ringer up as if you decloak then that 90% damage resistance I told you will not be there and if they have a Backburner or Phlogistinator with their crits enabled then you will become toast within seconds. Stay cloaked only taking minimal damage and retreat to friendly territory or into water, try to pick ammo packs up on the way as they will save your bacon, hopefully you will see a friendly Heavy and they will gun them down, if so, re disguise as a friendly like at the start and restart the process.
The Spycicle is a very useful knife when coupled with the Dead Ringer, when you see a Pyro you should swap to your Revolver so if you get flamed your knife will not melt. If an when you get ignited run away and swap to your knife and activate you Dead Ringer, this will con most Pyros as many new players play the Pyro and they usually aren't the brightest bulbs on the block. Note that you will not be able to do backstab anyone for 15 seconds, during that time I suggest that you look for metal to refill your Dead Ringer and look for a victim that's not near a Pyro.
Thanks to KiLlEr10312 for the suggestion
13) Capturing Control Points
All you need to do is break your disguise or disguise as a friendly team member, bring your Dead Ringer up and strafe at the area the enemy will most likely attack from. If your Dead Ringer is set off then get out of there, disguise as an enemy and backstab the person who triggered your Dead Ringer and contest the point again.
14) How to easily con people
If the team you're against keep on their toes when they strangely one hit you, follow this. When you need to set your Dead Ringer off, I suggest to hang around with 2 or 3 of your team mates (Medic and Heavy is a good choice) and hang around a few paces behind them. When you encounter an enemy hide behind one of your team mates, when they take some damage get out from behind them and take a hit, the person will not know that you are a Spy because: You are disguised as a friendly, they started shooting before you "died" and they got some hits on your small group. This is especially good is you walk into a Demo trap, they will notice they took 2 or 3 people out and aren't there to see who they killed, it is also perfectly logical to think your 8 sticky bombs killed a small group of enemies. Use this to your advantage, when a Sniper one hits you with his SMG then he is going to be a bit suspicious about a Spy being around. Use a group to cover up your Dead Ringer.
Thanks to KiLlEr10312 for the suggestion
15) The Saharan Spy
I recommend this set only to the top tier Spies as you are required to use the 'You Eternal Reward' (YER) and this makes it not possible to disguise at will, combine this with not being able to cloak at will then the odds are stacked against you to start. However if you do have this set then its bonus, being a lot quieter when decloaking, will give an amazing advantage as the decloaking sound of the Dead Ringer is blindingly obvious.
16) Things you shouldn't care about
HUD - http://code.google.com/p/eve-tf2hud/ The iRinger - http://www.gamebanana.com/tf2/skins/69346 Logo health - http://www.gamebanana.com/tf2/sprites/2421 The screens are from an offline practice match I did
EDIT: Re-worded some things and improved some grammatical errors, added KiLlEr10312's suggestions, made it look better, added what Dead Ringer doesn't replicate, paragraphed properly, numbered sections