XCOM 2 – What Hidden Abilities are Available?

There are 5 types of Experimental Ammo, and 3 types of Experimental grenades.

Ammo

As a side note, Ammo applies to Sharpshooter pistol shots.

• Armor Piercing - Bypasses an enemy's armor. No bonuses against enemies without armor.
• Dragon Rounds - Passive bonus damage and a chance to light targets on fire. (Enemies immune to fire can't be lit on fire, but still take the bonus damage)
• Talon Rounds - Reaper Rounds' big brother! +20% passive crit, and an extra +1 damage on critical hits. No extra range penalties like its predecessor.
• Tracer Rounds - +10 Aim while equipped.
• Venom Rounds - Passive bonus damage and a chance to poison the target. (Enemies immune to poison, like Chyrssalids, still take the bonus damage)

Grenades

• Acid Grenade / Bomb - Shreds more armor than a frag grenade, applies Acid to those hit, and leaves acid terrain tiles on the map for a few turns.
• Gas Grenade / Bomb - Larger area grenade that deals damage and poisons enemies hit.
• Incendiary Grenade / Bomb - High damage and sets enemies on fire.

And, though you didn't ask for it, why not --

Heavy Weapons

Heavy weapons are tiered. The "Heavy Weapons" become available once you unlock the E.X.O. suit, and the "Powered Weapons" become available once you unlok the W.A.R. suit.

Heavy Weapons

• Rocket Launcher - Unlocked by default. Deals explosion damage in an area & shreds armor.
• Flamethrower - Cone of flame to deal damage and ignite enemies.
• Shredder Gun - Cone of bullets to shred armor and cover.
• Blaster Launcher - Powered Weapon. Upgraded Rocket Launcher.
• Hellfire Projector - Powered Weapon. Upgraded Flamethrower.
• Shredstorm Cannon - Powered Weapon. Upgraded Shredder Gun.
• Plasma Blaster - Powerd Weapon. Linear area damage.

Here's an imgur album assembled by SYLOH with the in-game descriptions.

EMP Grenades/Bombs

So I just learned from Are Gatekeepers vulnerable to EMP Bombs? that Gatekeepers can actually be heavily damaged from EMP grenades/bombs, and can even have a chance to be stunned by them for 2 turns!

I tested and confirmed this myself. In the following screenshot, I used an EMP Bomb on an undamaged Gatekeeper, and it took something like 12 damage, and was also stunned:

Which is weird, because you can't hack a Gatekeeper, so who knew it had robotic components that could be damaged by an EMP?

Flashbangs

I've heard that Flashbangs (or being disoriented) can lower a target's Will stat, which would make it more vulnerable to mind control. I decided to test this out too.

The following is the Will stat of an undamaged Gatekeeper versus a fully upgraded (i.e. has all abilities and fully upgraded Alien Psi Amplifier) Psi Operative using Dominate:

The target's Will is 110%, which reduces my chance to Dominate to 80%. After hitting the Gatekeeper with an EMP Bomb, followed by a Flashbang (so that it's also Disoriented), I checked the chances again, and the Gatekeeper's Will was still 110%.

I've also heard that Flashbangs (and being disoriented) can disable some of the Gatekeeper's abilities, but I haven't tested this out yet, and I'm not sure which abilities exactly would be disabled.