I can't say "all", but many of the spells I've seen state "caster can
use/utilize any lower spell on this list each round". Or something to that effect. Not cast or even the old RM term, throw.
IMHO,
The one 50th lvl spell has already been cast. The effects of that one spell are the results of any lower lvl spell that the caster chooses. Like has already been said, PP have been spent. Caster can choose a different spell each round; max of 1 spell/rnd/lvl.
I wouldn't say that there is any chance of spell failure for the additional
effects because "the spell" (the 50th lvl spell) has already been cast.
It's like a Detect Essence 5'rad, 1 min/lvl. Instead of a different 5' rad, it's a different spell effect.
Do you use the original roll for all of the BAR/EAR effects..? Or do you make a BAR/EAR for each spell used? An awesome roll will make them all high (BAR/EAR), but a low roll on the initial spell would make them all weak. But making a roll per spell would open it up to failure (Unless the GM just wouldn't allow failure, since the spell has been cast).
Each spell would be just like normal, I guess. It would have full affects (duration/range/target..) as normal and the duration might last longer than the 50th lvl spell cast in the first place.
Some of the 50th lvl spells are Utility (which might be different than the lower lvl spells on the List; some are not) and even though it doesn't state it, I guess they actually affect the caster, granting the ability to utilize the lower lvl 1/rnd.
If one of those lower lvl spells are Parried/Canceled, etc by another spell, are they affected like a 50th lvl spell? That is the spell that caused their effects.
This is a great question and has me thinking more about the structure of magic in my game. Thanks.
I've never had someone cast a 50th lvl spell.