Combine Ace

Overview
Aces are some of the newest and most dangerous additions to the Combine force. While they may appear weaker than default Overwatch Soldiers with their jumpsuit-like armor, they are much faster, capable of running up to 3-4 times faster than Soldiers and Metrocops, as well as being able to perform very high jumps, often in places the player cannot reach. In addition, they actually have higher health than all other Combine humanoid units, having 100 health in total.

Behavior
Combine Aces are almost always alert, often running from place to place, attempting to seek out their enemies. The moment they notice one, they immediately begin to run around the area, firing away while they do so, rarely taking breaks in their sprints. Unlike Soldiers and other enemies, Aces will almost never fire in bursts, nearly always firing fully-automatically with striking accuracy.

If given the opportunity, Aces may begin to super-jump to very high up areas to throw off the player, which can prove to be a problem if the player has few weapons suited to long-range conflicts.

Aces usually carry MP5's, but may appear with other weapons as well, such as the default MP7 or AR2's. If the player is especially unlucky, they can also appear with Pulse Machine Guns on occasions.

Aces are often freakishly accurate with their weapons, often landing headshots on the player and causing untold amounts of aimpunch as a result, making counter-attacks quite difficult.

Something very unsettling about Aces is that they seem to have massively increased magazine sizes with their weapons, as they almost never have to reload. While most will run out of ammo with an MP5 within about 4 seconds, Aces are able to fire anywhere from 8-15 seconds straight, for example.

Thankfully, Aces almost never show up until the later chapters of the game (Anticitizen One, Nova Prospekt, etc.), and even when they do, they usually appear one at a time, albeit with other enemies coming to back them up.

Tactics
As Aces are very quick and usually don't stop moving, faster firing, moderate damage weapons are preferable, such as the MP40 or PMG. It is advisable to clear away any other enemies that may be in the area so they don't bother you, as having both an Ace and several Overwatch Soldiers on your tail at the same time can prove to be a serious problem.

Experienced players can try waiting until an Ace stops moving before quickly pelting them with a high damage weapon, such as a Karabiner 98 or Sawed-Off Shotgun. However, due to how short the intervals are between the Ace moving and stopping, this may not be the best idea.

Bullet Time can also be used to slow down the Ace, although this will slow down your bullets as well, so leading is often necessary.

If in a pinch, heavy weapons can be used to deal with Aces quickly, such as the Laser Rifle, although this is best saved as a last resort.

Trivia
Aces bear a striking resemblance to the Combine Assassin from the Half-Life 2 Beta.