Speed Plus, also known as Speed Source, Spd Up, and Speed, is a recurring item in the series. It first appeared in Final Fantasy VII, and last appeared in the 20th Anniversary of Final Fantasy. It permanently increases a character's Speed stat, and is thus a very rare item.
Only appears in Dawn of Souls and subsequent remakes found in the optional dungeons, Hellfire Chasm, Whisperwind Cove and Lifespring Grotto. It is bugged in the GBA/PSP versions; for every 1 Agility gained via Speed Plus, only 1 Evasion is gained on the character, as opposed to 2 Evasion for every 1 Agility. It is unknown if this bug was fixed for mobile versions.
Speed Sources permanently raise the Speed stat by one. It can be morphed from Poodler, found in Junon, Gaea's Cliff, Northern Cave and as a prize from the G-Bike game in Wonder Square by winning with over 10,000 points.
Spd Up can be obtained by using Doomtrain's Forbid Med-RF ability to refine Aegis Amulet x2, Jet Engine x50, Rocket Engine x5 or Hundred Needles x1 into Spd Up x1 each. One can also be found under Zell's pillow by completing the Big Bad Rascal quest.
This item is called Speed and it has a potion icon before its name. It can be found in assorted treasure chests throughout the various worlds and increased a character's Agl stat by 3. It's also a one time use item as opposed to other consumable items which have more uses. Only only usable on humans or mutants.
The Speed item is a Robotic Parts that gives a permanent stat increase to Agility by 3, but it can only be applied when the character is a robot. If said character changes forms, they'll lose the stats gain through this item. It can be bought for 1500 GP in Cirrus, Dharm (Present), Donmac, Elan (Past and Future), and Knaya.