Shyvana gets removed from the game. Sejuani gets reworked to this. Anyone that owned previous Shyvana skins get them as the new Shyv/Sej hybrid.
Passive: Basic attacks do something to all abilities. Q: Dragon leap, Sejuani Q without the stopping at enemy champions. AA reduces CD. W: Burnout/Northern Winds. Burnout scales with bonus AD + AP. Northern Winds scales with HP. Only does the strongest one. AA increases duration. E: Dragon's Breath. (FIre or Ice). Fire scales with bonus AD + AP and lowers enemy armor/Mres. Ice scales with HP and causes the enemy to start slowing in an area around them. AA will either keep decreasing armor/MRes over the duration or start increasing the slow. Works same as W for choosing which one activates. R: Dragon's Roar/Glacial Prison: Shyvana lets out a large AoE nuke of her fire breath that burns over time. Sejuani throws her weapon that stuns enemies around where her weapons explode. Both ults work the same as Sejuani's current ult. Works same as W for choosing which one activates. AA someone debuffed by Dragon's Roar will eventually stun them, slowing them down with each hit. AA someone debuffed by Gracial Prison starting doing 5% of the spells damage. (Damage increases on each continuous AA, so 5-->10-->15, ect).
Shyv/Sej scales off Bonus AD+AP OR bonus HP, not both. It is the balance that much be found if you want more CC on your team or more damage with Armor/MRes shred.