Helix

Helixes appear in the fight against Ultimecia-Griever. What precisely they are is unknown, but by some method they apparently provide a boost to Ultimecia's magical powers.

Battle
At any rate, Ultimecia summons Helixes one at a time in the third stage of the final boss battle in Final Fantasy VIII. Helixes don't do much themselves; they might fire off a Double Laser counterattack every so often, but that's about it. Once they appear, however, they give Ultimecia the ability to use the spells Ultima and Meteor and the skill Great Attractor, which is nothing to be sneezed at. They are also quite evasive and difficult to kill, making them a pain to deal with. Fortunately, they automatically disappear once Ultimecia loses about 65% of her maximum HP.

Theory
The most likely theory seems to be that they are objects created by Dr. Odine, who has extensively studied Sorceress power to the point that he has even created jewelry that can prevent a Sorceress from using her magic. It thus seems likely that he could have created the opposite--a machine that could amplify a Sorceress' magic--although it is also possible that a Helix is a machine from the future that was built off of Odine's research and brought back to the past by Ultimecia.