Actually, I was quite surprised that I found no other thread regarding favorite spells since it’s a very basic question relating to a RPG which focuses on magic. I apologize in advance in case I have overlooked similar topics.
What are your favorite spells in ArM? Which ones do you believe to be almost indispensable for most of your character concepts? Which ones do you consider immensely useful or perhaps even borderlining on overpowered for their particular level? And which ones do you simply love for being extremely atmospheric? In case you use certain spells in rather quirky, unconventional or non-obvious ways to utilize their full potential, please be so kind to share them. Either existing formulaic magic or your own creations are fine.
My personal favorites so far are:
Veil of Invisibility (PeIm 20)
While this may be no especially unusual choice, it’s hard for me to imagine a magus outside of his covenant who can’t put this spell to good use: It’s useful in combat against wild animals, mundane foes and other wizards alike. It gets you out of precarious situations. It boosts your stealth allowing you to infiltrate and to eavesdrop. Furthermore, you can cast it on your allies to set ambushes or let them do your dirty work.
Image Phantom (MuIm 20)
This one is almost too good to be true for a creative player! The ability to change the appearance of any inanimate or living thing allows for endless possibilities: What was once your trusty grog is now the emperor of the Holy Roman Empire! That lump of rock? It’s gold, obviously! Change your appearance to escape your foes or to set elaborate traps for them. Impersonate your enemies to create all sort of mischief. Few other spells come close regarding flexibility.
Wizard’s Leap (ReCo 15)
Close-range teleportation is one of the most useful abilities to have in my opinion and is - once again - a lifesaver in a lot of situations. You want to keep out of harm’s way? Wizard's Leap! Position yourself effectively on the battlefield? Wizard’s Leap! Pass an obstacle like a river, a chasm or iron bars? Wizard’s Leap!