Thunder Shield

The Lightning Shield (a.k.a. Magni-barrier) is a power-up item from Sonic the Hedgehog 3, as well as its locked-on form, Sonic 3 & Knuckles. It is obtained by destroying an item box with a lightning bolt symbol (pictured) or by obtaining a gold-colored gumball in the Bonus Stage.

Sonic 3 & Knuckles
The shield absorbs one hit, as well as allowing Sonic to perform a double-jump. Like the Fire Shield, Sonic will lose the shield if it touches water, but the water will flash for a split second, representing the electricity being dispersed in the water. Strangely, the shield is not lost when the player's character skims across the surface of the water in the Hydrocity Zone. Also, like the Bubble Shield and Fire Shield, this shield will deflect shots from badniks that use energy weapons (such as Blastoids) but not lasers. It is also magnetic, as it attracts rings.

Other games
The Lightning Shield has also appeared in games such as Sonic Adventure and Sonic Rush. In these games, the shield is blue and has a plasma ball effect, but does not give the player a double-jump.

This shield appears, along with the Fire Shield and a normal shield, in Shadow the Hedgehog. It can be acquired as a power-up from boxes or activated by breaking an item box. It functions by magnetizing nearby rings into Shadow and disappears when Shadow gets hit, or when he dies by falling.

A version of this shield appears in Sonic the Hedgehog (2006) in the form of an ability, Thunder Guard. This ability can be activated using a Yellow Gem.

The shield appears in Sonic Generations as the Thunder Shield. After completing a certain mission for City Escape, Classic Sonic is able to buy the Thunder Shield as a Skill at the Skill Shop. It costs 4000 skill points to buy and 70 points to equip. The shield retains all of its abilities from Sonic 3 & Knuckles,  but the shield does not disappear when the player goes underwater. There are also glitches where if a player activates the double jump ability while jumping on certain springs, it would either bounce the player into an explorable part of the map with nothing in it or it will send them falling to their death in a bottomless pit.

In the 3DS version of the aforementioned game, the Lightning Shield functions the same as in Sonic Adventure and Sonic Rush. It can only be found in Act 1 of Emerald Coast. However, it can also be obtained as an extra skill by playing Versus Mode online.