King's Rock only affects damaging moves that don't already have a flinch rate (ex. Blizzard); it does not increase the flinch rate of moves that already have that ability.
Something I have been using with a lot of success is DD Mix Latios
Latios (M) @ Life Orb Trait: Levitate
EVs: 240 Atk / 16 SAtk / 252 Spd
Hasty Nature (+Spd, -Def)
- Outrage
- Draco Meteor
- Earthquake
- Dragon Dance
Given EVs for Max Speed to speed tie other Lati@s. Rest to hit 276 Atk and 300 SpA, these are just arbitrary numbers spawned by my OCD need for significant numbers. The idea is to come in on something you can force out, and then get a DD. After one Dragon Dance, Latios can speed tie even Scarfed base 110s. Once enemy Steels are removed (Magnezone or even Heatran support is crucial to this set's success, if the opponent has a Scizor, this set is completely shut down). Outside of Steels, almost nothing can take a Draco Meteor AND an Outrage- only one of the two, the other will hit it very hard. Also key to this set's success is bluffing. Any sort of Physical Latios is totally unexpected, so if you can bluff as a Special Latios by just using Draco Meteor at first, eventually they will send in a Special-based Pokemon. (Ex, Volcarona, who has taken as much as 80% on the switch-in). Alternatively, you can reveal that it is a DD set right off the bat, and wait for them to send in a Physically-based Poke, but this isn't as effective. Earthquake is there for Heatran and for general coverage, but if you really hate Scizor, HP Fire is an option.
This set has a few advantages over Salamence and Dragonite.
1. It is not weak to Stealth Rock
2. Unique typing means it takes Special Hits better at the cost of more Physical weakness.
3. Higher speed
4. Greater surprise value
5. With an alternate EV Spread, Latios is capable of higher SpA, but it will more or less need to get a Dragon Dance up to hit hard Physically...