TAG
TAGs, or Tactical Armoured Gears, are Infinity's version of Mechs, walkers, tanks, Tachikomas, Metal Gears and what have you. Designed to suit the doctrine of war in the Infinity setting, they're expensive but destructive as hell models that tend to serve well as Lieutenants or as centerpieces of your forces. Model-wise, they're two or three times bigger than most other models on the field and tend to be faster and more durable than most infantry. Since Infinity doesn't run tanks, planes, Warjacks or Carnifexes, they're likely to be the scariest things on the board when they appear.
Fluff
TAGs are high-mobility, highly armoured vehicles designed for durability and mobility. Many depicted in Infinity are humanoid, others such as Haqqislam's Maghariba Guard look like a spider tank right out of Ghost in the Shell/Appleseed. Different factions have access to different styles and numbers. PanO, for example, has SEVEN possible TAG models, where as Haqqislam has one, and Ariadna has zero. TAGs are amphibious, suitable for space or land based combat, virtually silent and capable of shrugging off small arms fire. However, as advanced machinery they're vulnerable to being hacked.
Some TAGs are directly piloted by a driver sitting in an internal cockpit. Others are "remote presence", piloted via an AI or otherwise don't contain a human occupant. The Combined Army fields TAGs which are an aspect of the EI, their controlling Artificial Intelligence, controlling a mechanical body.
Gameplay
TAGs are Bad News. While they'll usually take up about 1/3 of your available points in a large match, their stats are enough that fighting them without a specific Anti-TAG unit generally won't bear fruit. The Marut TAG fielded by ALEPH, for example, will shrug off 75% of incoming Combi-rifle rounds and can take 3 hits before being disabled. That means that a Marut will usually need to take 12 direct hits before going down. TAGs also can be used to control Remote units such as drones, as a distraction if you can take the points cost, and a variety of other things depending on what gear you give them.
On the downside, TAGs are expensive. A model costs somewhere around $40-60, and in points average somewhere between 80-110 in a game where 300 points is a "large" force. Nomads get some cheap ones at 50-90 points but even then you're taking a substantial hit to your force composition to bring one along. Weapons such as Hacking Devices, Adhesive Launchers and Panzerfausts will make short work of your wannabe Gundam, they're too limited to run in Linkteams, they don't fit through doors and certain special ammo types will RUIN their day.