Twin Bites flat cooldown reduction is not effective against structures.
The only exception to Dragon FormTwin Bite applying on-hit effects to all affected targets is Tiamat and Ravenous Hydra's passive effect Cleave, as it has an internal cooldown of 0.05 seconds when triggered on different targets. This is a special case to prevent abuse.
Active:Shyvana surrounds herself in flame for 3 seconds, dealing magic damage to nearby enemies each second, increased by 20% against monsters, and gaining bonus movement speed which decays by 15% of its original value each second.
「 Magic Damage Per Second: 20 / 32 / 45 / 57 / 70 (+ 20% bonus AD) 」「 Magic Damage Per Second Against Monsters: 24 / 38.4 / 54 / 68.8 / 84 (+ 24% bonus AD) 」
Dragon's Descent has an effective duration of 20 seconds when not attacking. When permanently attacking at 2.5 attack speed, it has an indefinite effective duration.
Dragon's Descent has an effective cooldown of 150 / 75 / 50 seconds when not attacking. When permanently attacking at 2.5 attack speed, it has an effective cooldown of about 17.65 / 15.8 / 14.3 seconds. Combined with Sated Devourer, the effective cooldown is reduced to 12.24 / 11.32 / 10.5 seconds.