Pokémon Type Advantage Modifiers

I'm looking for a list of any item, move, ability, etc. that would modify the standard type advantages in Pokémon up to and including ORAS for Nintendo 3DS.
For example:
Typically, Bronzong (Steel and Psychic type) would be weak to Ground type attacks since Ground is super effective against Steel, and Psychic is neither weak or strong to Ground. However, if Bronzong has the Levitate ability, he becomes completely immune to all Ground attacks.
If the opposing Pokémon uses the move Smack Down, however, this allows Bronzong to be hit by Ground-type moves again.
I'm working on a personal project to create an applet to calculate many things Pokémon, including potential type advantages in many different situations.
Can anyone enumerate these for me?
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Which Pokémon type has the most advantages?
1. STEEL :- Steel types pokemon are defensively OP having 10 Resistances : Normal, Flying, Rock, Bug, Steel, Grass, Psychic, Ice, Dragon, Fairy and immunity to Poison. They have good attack and amazing defense stats overall.What are the Pokémon type advantages?
Pokemon Type ChartTypeAdvantage OverDisadvantage ToGrassWater, Ground, RockFire, Ice, Poison, Flying, BugRockFire, Ice, Flying, BugWater, Grass, Fighting, Ground, SteelIceGrass, Ground, Flying, DragonFire, Fighting, Rock, SteelDragonDragonIce, Dragon, Fairy14 more rows•Oct 22, 2020What are the 18 types of Pokemon?
There are 18 Pokemon types in all: Normal, Fire, Water, Grass, Flying, Fighting, Poison, Electric, Ground, Rock, Psychic, Ice, Bug, Ghost, Steel, Dragon, Dark and Fairy.Pok pok pokat.....
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