You only asked for Custom Spells, but I'm giving you EVERYTHING including strategies, so pardon me if this is a bit long.
Robe: Robe and Hat
Color: Red
Favorite Staff: Staff of Emergency Teleport
Favorite Weapon: A60
Favorite Overall Element: Arcane
Favorite Chapters/Areas: Chapters 2 and 3 (good for practicing spell combos), Chapter 5 (all), Chapter 8 (before entering Jarn Mines)
Favorite Boss Fight: Battling Grimnir during and after the Mind Duel.
Favorite Joke: Try summoning a Pheonix indoors. The Pheonix will be eternally grateful!
Favorite Offense Spells:
Favorite Spell> Rock Arcane (D Sx1-4 based on enemy count and allied presence)
Rock (Dx5)
Rock Arcane Fire (D Sx2 Fx2)
Rock Fire (D Fx1-4 based on enemy count, allied presence and allied and enemy fire resistance)
Steam Lightning Arcane (QF Ax2 Sx2) (Make sure Steam is made before you use Lightning. I don't use this against enemies with Lightning resistance)
Favorite Beam> Arcane Cold Lightning (Sx2 R Ax2)
AoE Arcane (Sx1-5)
AoE Ice (QRx1-5)
Favorite Defense Spells:
Favorite> Shield Rock; AoE Shield Rock; Self Shield Rock (E Dx4)
Shield Rock Fire; AoE Shield Rock Fire (E Dx1-3 Fx1-3 based on enemy count and their fire resistance. More enemies=more Fire while more fire resistance=more Rock)
Favorite Magicks:
Teleport, Nullify, Lightning Bolt (not Storm), Favorite> Summon Elemental (Arcane or Lightning), Conflagration
Favorite Strategies:
Freezing: My ultimate favorite has to be freezing your opponents with Water mixed with Arcane or Rock, followed by Cold, also mixed with Arcane or Rock. Steam doesn't knock back and deals damage while Water is easier and faster to cast, but both wet. I personally preffer Water. This works best with a 2nd person so one can wet and the other can freeze in 1 spell combo.
Fire: When goblin bombers are present, I do not hesitate to use Rock Fire or Rock Arcane Fire as described above or Conflagration. If I can make them explode, I just wiped out a good number of enemies.
AoE: I try not to AoE for the sake of my allies, but I will if necessary for my survival.
Lightning Bolt: I play it smart and safe with Lightning Bolt. I don't use it unless my allies are behind me or my target is definately higher elevated. I NEVER use Lightning Storm because there is a good possbility lightning WILL strike me.
AoE Rock: I always use AoE Rock (Dx5) against enemies with hand-held shields to disarm them, making them much easier to kill. It's not my favorite spell, but I know how effective it is.
Elementals: It's my absolute favorite Magick in the game, but I only use this spell as a last resort because I like the challenge of kiling the enemies myself. If I can't, I spam Arcane Elementals. In the missions, there's this 1 area I spam Elementals. A Beholder is present, so to counter him, I use Lightning Elementals. In the challenge, I have yet to survive all waves, so this spell is a must-get for me along with Invisibility. I use Arcane Elementals so I can use my favorite spell, Rock Arcane, to deal damage to my enemies AND heal my own Elementals while staying away from combat.