I hope I did this stuff right...
- What are common secondary moves in today's metagame?
Leech Seed, Will-O-Wisp, Toxic, Thunder Wave, etc.
- What does it mean to "Stop the Secondary"?
To prevent or negate special effects, etc, with abilities and moves such as Cloud Nine, Rapid Spin, etc.
- What are the possibilities of this CAP? (Try not to poll jump too much here)
Rapid Spin can remove Leech Seed, and entry hazards. Psycho Shift can remove status and send them back at your opponent. Abilities such as Guts, Quick Feet, and Synchronize can hinder your opponent for inflicting status on you.
- How are immunities used in the current metagame? How can we apply that knowledge to this project?
Immunities are often used to switch into attacks, and either increase the chance for your opponent to use a different attack (If you were, say, battling a Dusknoir with Shadow Punch/Focus Punch/Earthquake/filler [bad example, I know], and you had a Heatran, Gengar, and a Blissey, you could switch to Gengar on the Earthquake, then to Blissey on the Shadow Punch, and you would then be able to use Toxic while Focus Punch can only say, 2HKO you, while you can stall with Softboiled or attack with Ice Beam) or to block the move and take them out (If something like a DDed Gyarados is out against a Magnezone, you can switch in something like a Scarfed Gengar in hopes of them Earthquaking, and can kill them without sacrificing Magnezone).
- What do we gain from an immunity pokemon?
We gain the capabilities to switch into attacks, and supporting our team by removing secondary effects that may hinder them, such as a Sashed Pokemon hating entry hazards and weather effects, while with them out of the picture, it could be deadly.
Also, looking at moi's list as well, these are what I've thought of:
Sleep: Vital Spirit, Substitute, Insomnia, Taunt, Safeguard, etc.
Poison: Poison-type, Immunity, Substitute, Taunt, Steel-type, Safeguard, Magic Guard, etc.
Paralysis: Safeguard, Limber, Ground-typing (for Thunder Wave), Ghost-typing (for Body Slam), Quick Feet (but you still can be fully paralyzed), Volt Absorb/Motor Drive (for Thunder Wave), etc.
Confusion: Own Tempo, Safeguard, etc.
Attract: Oblivious, Genderless Pokemon, Taunt, Substitute, Safeguard (I think), etc.
Burn: Water Veil, Guts, Flash Fire, Fire-type, Substitute, Safeguard, Taunt (for Will-O-Wisp), etc.
Freeze: Magma Armor, Substitute, Safeguard, Shield Dust, etc.
Stealth Rocks: Rapid Spin, Rock-resistance (to weaken it), Magic Guard, Mountaineer, Taunt, etc.
Spikes: Flying-type, Levitate, Rapid Spin, Magic Guard, Taunt, etc.
Toxic Spikes: Poison-type, Steel-type, Rapid Spin, Levitate, Flying-type, Taunt, Magic Guard, etc.
Weather Conditions (Hail, Sandstorm, Rain, Sun): Ice-type, Rock-type, Steel-type, Ground-type, Ice Body, Sand Veil, Magic Guard, Snow Cloak, Magic Guard, Air Lock, Cloud Nine, etc.
Gravity: Taunt, etc.
Trick Room: Low speed, Taunt, Trick Room, etc.
Trick: Multitype, Taunt, Klutz, Sticky Ooze, etc.
Taunt: Faster Taunt, not using non-offense moves, OHKOing them before they attack, etc.
Encore: Taunt, being Choiced, etc.
Leech Seed: Rapid Spin, Grass-type, Liquid Ooze, Substitute, Taunt, etc.