Section 1. Overview
-Estimated Trophy Difficulty: 7.04
-Offline Trophies: 47 (38 8 1)
-Online Trophies: 3 (1 1 1) unobtainable due to server closure
-Approximate time to /100%: 25 - 50+ hours unobtainable due to server closure
-Minimum Number of Playthroughs Needed: 1 (Recommend 3)
-Number of Missable Trophies: Zero
-Glitched Trophies: None
-Do cheat codes disable trophies: None
Section 2. Introduction
Red Alert 3 is the latest in the Red Alert series and the biggest innovation it brings is the co-op commander which is where the 3 online trophies come from. The game itself requires only 1 playthrough, but achieving that is a lot harder than it sounds.
First you need to find yourself a competent co-commander and complete every mission on hard while not missing any of the secondary objectives. The hardest thing about this is some missions are brutal on both players, you CANNOT save your game in co-op play and some missions (and other secondary objectives) have a timer; so if you miss it you'll have to do the entire mission all over again. For safety, I will be using the 3 playthrough method in this road map.
Section 3. Walkthrough
Before we begin I advise utilizing this guide written by Raining Metal at Gamefaqs.
Whether you're new or a veteran of the RTS genre, play through all 6 tutorials for your first trophy. All it entails is the computer telling you what to do and how to do it.
Step 1: Story Mode Playthrough 1
Set the difficulty on Medium, this is your basic playthrough. You'll get all storyline related trophies as well as "Tempus Fugit" when you're finished. Use this playthrough to get a feel for the missions and knock out as many Secondary Objectives as you can. I recommend writing down missed objectives if you're not focusing on them. If you're confident in your RTS abilities then this playthrough can be skipped.
Step 2: Story Mode Playthrough 2
Set the difficulty to Hard, this is your "Master and Commander" playthrough. Don't feel obligated to hit Secondary Objectives here. Your focus should be only the Primary Objectives, but if you haven't completed all of the Secondary Objectives you can work towards them as well. I advise using multiple saves for each mission as some of them are extremely difficult.
Step 3: Story Mode Playthrough 3
This playthrough is your co-op playthrough. Find a partner here and hit the missions on Easy mode. Your partner will probably want to play through all the missions on Hard, but if they are not skilled and don't know what to expect, I strongly suggest you refuse. Some missions (i.e. Allies 9) are extremely difficult and without the ability to save, your attempts will be infuriating. Use this playthrough to grab any Secondary Objectives you may be missing.
Step 4: Skirmish Mode (Unit / Kill Trophies)
Most of the trophies here are for killing a certain number of units a certain way; some are more difficult than others. While they are all able to be done against the CPU, a boosting partner is highly recommended (boosting thread is here). If you can get two partners on at the same time, all three of you can attain every trophy in one battle. Each one of you will have to be a different faction and let your partners capture a MCV so they can make units specific to a trophy. Check the trophy guide for details.
Step 5: Skirmish Mode (Map Trophies)
With all the technical skirmish trophies out of the way there's only a handful left. One is to beat all of the AI commander personalities on a 1-vs-1 map. Another is to win a skirmish on every map (27 maps in total). Those are the most time consuming trophies. The only other ones you should be missing are to win a 3-on-1 match, beat a brutal difficult opponent and win a match in under 5 minutes. Details for the last three trophies can be found in the trophy guide.
[PS3T Would Like to Thank Kheapathic for this Road Map]