N.B. This is not a complete morph list. It aims to feature the more significant items you can morph in Final Fantasy VII only.
The "Morph" command does considerably less damage than a normal attack, but if it kills the enemy, the enemy may change into an item. For easier results use characters' ultimate weapons; these will deal approximately 1/3 damage of a normal attack while morphing rather than 1/9. You can find details of ultimate weapons here.
The exceptions are Yuffie's Conformer, which deals full damage even when morphing; Barret's Missing Score, which can work well with enough high AP materia in it; and Vincent's Death Penalty, which is effective after Vincent has killed enough enemies.
You can find the "Morph" materia in the Temple of the Ancients.
Source items are a great way of making your characters ultra powerful in FF7. You will pick up a few as you play through the game, but really making good use of them will require a lot of patience and clever use of the Morph command.
There are 2 great places to find stat sources in Final Fantasy VII. The first is the exploded reactor in Gongaga; here you can morph Heavy Tanks for Power Sources. They're very easy to morph in just one hit once your level is quite high.
The second place is the Sunken Gelnika, the crashed airplane which you can explore underwater once you have a submarine. Each of the enemies here can be morphed into a different stat source: Power Sources, Magic Sources, Guard Sources, Mind Sources, Speed Sources, & Luck Sources. These cover all 6 of Strength, Magic, Vitality, Spirit, Dexterity and Luck. As mentioned earlier, you are advised to equip characters' ultimate weapons while doing this.
To use a source, just enter the Item section of the menu, select the source, and choose a character to use it on. The maximum a stat can reach is 255. However, you can give a character a fair few more sources even once a stat is at 255 before the game won't let you give any more. This is probably because even with a stat at 255, it would drop below 255 with certain materia equipped.
So a character with 255 Dexterity and a Mystile equipped has a Defence % of 113. Also note that the Dexterity stat also affects the speed at which your time gauge fills up; at 255 Dexterity, it will be fast.
One further thing of note: with Magic at 255, Knights of Round will take off 9999 or very close to it with every hit, without needing to be linked to an MP Turbo materia.
And last but not least, you may be wondering which of your party members it makes most sense to give sources to. Sources are good for any party member; but given that for most of the game Cloud is a default party member, it makes most sense to give sources to Cloud!
Find this Morph Guide useful? Why not check out my Steal Guide?!
Limit Breaks Guide
Enemy Skill Guide
Final Fantasy VII Remake Guide
List of Every FF7 Title
Other FF7 Websites