Hugo and King are the latest members of the Street Fighter x Tekken Mobile cast. Here's some artwork and screens:
Capcom also detailed a couple of gameplay systems from the iPhone crossover fight: Gem Roulette and Partner Gauge.
The "Gem Roulette" system releases a "Pandoras Box" when you connect a launch attack (-> + X). This contains a random gem.
The "Partner Gauge" system is used for your sub character. The partner gauge depletes when your sub character takes damage. When empty, you'll be forced back to your main character.