The Speed Reducing Mega Armor is an ability given to the Cybran Loyalist Assault Bot. It's unlocked by Reserch. Like the names Says, it increased so seriously, so that the Loyalist is really slowed down.
The best way to use this is to go into an enemy base, and shortly after you enter the base Activate this ability, so that the Loyalist Assault can take less damage thus giving it more time to deal damage back. Remember this ability has (like the most abilities) a cool down time. So if you activate it to early, your units are too slow for effective attacking. Slow units are easier to eliminate with longer range units such as UEF or Aeon Illuminate tanks (using micro) or an experimental with a longer range, so only activate it only when you enter a base or near an experimental (better if you have Fast Walk ability to catch up and surround your enemy then activate it) if used correctly this can turn the tide of any battle.