Mags are useful in most certain places. Your PB (Photon Blast) Gauge will increase when you strike an enemy, get injured or equip a PB Unit.
If you transfer your high leveled mag to your other low leveled character, the PB Gauge will rapidly increase (said above) when you equip it. When the PB Gauge is full, press and hold CTRL and you can see at least 3 Photon Blasts you can use. They are:
-Mylla & Youlla
You can get these cool Photon Blasts depending what you are feeding it. It is also to donate PB before the Photon Blast starts.
When a player used a Photon Blast, I rapidly press the END Key to donate my PB. It cost 10% of your PB, that equals only 10 PB. If were gonna do "GROUP PHOTON BLAST" we all have to use our Photon Blast at the same time. The number will appear beside your HP/TP (same for other players), the number that says 1 gets to use his/her Photon Blast first. The faster you act, you will become first to use the Photon Blast. This only happens when your PB Gauge is 100. If you do not have 100 PB and someone just used a Photon Blast either you donate for power or watch helplessly.
Two Photon Blasts can support you by healing or get buffs on.
Mylla & Youlla: They have the power to give you buffs, Shifta & Deband(not debuffs, Jellen & Zalure). If you donate while you are dead, you can be resurrected and continue the battle. This is most useful to most players.
Leilla: She has the power to heal, if people donate they will get healed, too. Not only that their status ailments will also be removed. If you donate while you are dead, you can be resurrected and continue the battle. Mostly FORCES have this Photon Blast.
Feeding mags is easy, just press F4 and a Feed Mag Menu will appear. When feeding mags you will see stats go up. Some stats poorly increased because it's not its favorite kind of food. And you will also lose some recovery items. As long you have Resta and Anti (and other supportive spells) you won't need those items (but you will need it if TP runs out).
Here are the stats for the Mag:
DEF - Boosts your DFP by 2 every time it levels up (Gain more resistance of the enemy's attack)
POW - Boosts your ATP by 2 every time it levels up (Able to use better Swords)
DEX - Boosts your ATA by 1 every 2 level ups no this stat (Able to use better Guns)
MIND - Boosts your MST by 2 every time it levels up (Enhances Technique Power and able to use better Canes)
Here is the items you can raise those stats:
Monomate - Raises moderate of POW
Dimate - Raises greatly of POW
Trimate - Raises massively of POW and a little DEF
Monofluid - Raises moderate of MIND
Difluid - Raises greatly of MIND
Trifluid - Raises massively on MIND and a little DEX or DEF
Antidote - Increase DEX
Anti-Paralysis - Increase DEX
Sol Atomizers - Raises POW/MIND & DEX depending on Mag
Moon Atomizers - Raises POW/MIND & DEX depending on Mag
Star Atomizers - Raises all stats greatly on baby Mags and poorly on strong Mags
There's also another way to evolve Mags without feeding. There is a special item known as "MAG CELLS" they are used on Mags on certain conditions. Mag Cells can create different forms rather than the ones on the gallery you've seen. Also those Mags abilities triggers if you are Dead, Full on PB Gauge, Entering the Boss and Low on HP.