This can be found in the Events button top right as the first tab. You get 3 chests every 4 hours and 3 bonus chests daily. You should try to open as many of them as you can every day. These chests contain valuable Skill Medals which are a rare resource for increasing the power of your heroes.
Hero Advancement
This is the easiest one especially once your HQ is 20 or above. You simply chose a hero and click upgrade. At hero level 100 it takes one upgrade to get all 3 chests.
City Building
Use your construction speed ups first to gain as many points as you can. Only complete constructions (open presents) if you run low on speed ups as you want to save completions for VS days 2 and 5. Try not to use universal speed ups unless you are close to getting the last chest.
Unit Progression
You get points here for starting and using speed ups but not for completing training. You can complete training before, during, or after.
You should have 2 barracks at your max troop level and 2 barracks at one level below that. For example, at HQ 27, have 1 barracks at level 19 that train level 6 troops, 1 barracks level 20-23 to train level 7 troops, 1 barracks at level 24-26 to train level 8 troops, and 1 barracks at level 27 to train level 9 troops. I will use these levels for the strategy below.
- prepare beforehand by training troops in all 4 barracks at level 5
- complete all 4 barracks to release the troops
- use the level 19 barracks to promote them from 5 to 6
- use speed ups to quickly complete the training and release them
- use the level 20-23 barracks to promote the level 6 troops to 7
- use speed ups to quickly complete the training and release them
- use the level 24-26 barracks to promote the level 7 troops to 8
- use speed ups to quickly complete the training and release them
- use the level 27 barracks to promote the level 8 troops to 9
- use speed ups to quickly complete the training and release them
- repeat steps 3 through 10 until you have all 3 Arms Race chests (Save the extra level 5 troops for next arms and/or VS day 5)
- finally, use all 4 barracks to train new troops to level 5
This strategy works extremely well for VS day 5 and 6, however, you would continue repeating the steps until all troops are trained in order to get all the VS chests as well.
Tech Research
Use research speed ups and complete tech research until you have all 3 chests. Planning ahead by checking when this Arms Race will come up and having your research end close to this time helps. Try not to use universal speed ups unless you are close to getting the last chest.
Drone Boost
Only use Drone Battle Data and Drone Parts when this Arms Race overlaps with VS. Otherwise, run 15 rallies to burn 300 stamina to get your chests. Save your Drone Battle Data and Drone Parts for VS Day 1.