Same tough armor of the Longhorn, but trades its heavy cannon for faster firing lighter weapons. While it may not have the same stopping power as the Longhorn, it has got a fast fire-rate and gun rotation, making it strong against light units.
The Gemini is a modified assault tank with rapid-fire cannons. Although the damage is reduced against heavily armored targets and it is outmatched by that of a Longhorn the Gemini makes up for it with quick damage dealing against light targets.
Gemini have a low weapon rating but a high rate of fire, allowing it to deal large amounts of damage to all types of units, especially light units.
It's relatively high HP to build cost ratio makes it efficient for pushing into enemy defenses.
Good tank for defends against Mechs because of the high turret rotation speed.
Doesn't do much damage to other heavy tanks.
It has a slow build speed and high cost, making it difficult to quickly replace a destroyed army.
Gemini works best in loadouts consisting of Anti-Air to protect them from infantry and enemy AirMechs.
Gemini have increased survivability with support from damage soakers such as Turtle, and Repair units.
Equal to the Longhorn in terms of speed, price, build time, and armor, but different in function due to the Mounted Light Cannons rather than a heavier, anti-tank cannon of the Longhorn. Gemini cannons fire smaller, lighter shells that deal less damage to targets, but the cannons also fire roughly twice as fast as a Longhorn's, and to supplement, the Gemini's turret also can turn slightly faster than that of a Longhorn.
Gemini provide a counter-counter to light units such as Jackal or Bucky, which slower-firing tanks like Armadillo and Longhorn may have a harder time dealing with in larger numbers. Other tanks may deal more damage per shot against light units, but this damage is dealt over a much longer time due to longer reloads. Gemini on the other hand fire much faster, allowing the to have a higher damage per second against Lighter units, thus being more effective.
Gemini are great at assaulting outposts due to their light weaponry, yet heavy armor. A gemini can deal damage more effectively against infantry than any other tank. Gemini, as such, can neutralize outposts faster than any other tank, and is typically more cost effective than sending light units against an outpost.
The tradeoff here is that while Gemini is excellent against lighter units and infantry, its lighter weapons do not deal heavy damage to other tanks, especially Longhorn, regarded as Gemini's counter. Equal numbers of Gemini and Longhorn will more than likely favor the Longhorns.
But more importantly than fighting similar-tier tanks is fighting the higher-tier tanks and units, such as Goliath, Devastator, Grinder, and T99. While those units are strong against tanks in general, they become stronger against armies composed of Gemini, as Gemini lack the higher-grade weapons that Longhorns, and even Armadillos may have. Small and select armies of Longhorns, and scattered armadillos can provide good defense against Armored units, but Gemini will have a tougher time piercing the heavy armor, and thus suffer larger casualties.
In a nutshell, Gemini are great at the early game, capping outposts and demolishing Infantry and lighter vehicles, but become much less powerful as the game progresses, and stronger units are fielded. Make sure that you pack support units in your loadout if you wish to main Gemini, such as Bucky or perhaps Longhorn, so offset the lack of armor-piercing power.