It gives Aftermath: Shock Spikes.
The Shock Spikes deal 14-18 damage, even on the level 95 version. The Shock Spikes almost never proc stun on anything above EP.
Awful. Terrible. Worthless. Lame. Worst aftermath effect ever.
Suggestion: Replace this aftermath with: "Additional Effect: Damage varies with Wyvern HP."
Efffect: With aftermath on, attacks have a 10-15% chance to add non-elemental damage equal to 1/4 of the Wyvern's current HP, similar to Excalibur.
Animation: An enthunder animation, to keep the lightning/thunder theme of Gungnir's lore/history/mythology.
This changes Gungnir's Aftermath form being a passive/defense boost and makes it more offensive. Also because...SHOCKSPIKES?! REALLY?! COME. ON.!!!