((I have an idea for a system of ritual.
Since Rituals Are Meant To Take more Time And Preparation, The Shortest Basic Ritual Takes 2 Turns.
In The First Turn, A "Head" Mage states what the spell casted will be in the ritual (This can be public or private).
Once this is done, All Mages Participating in the ritual may choose to sacrifice items, shards, essences, etc. to help power up/ improve the chances of success for the ritual. (This works the same way as when casting quick spells).
Next, a roll is done for Potency and Luck using a D6<0 - 5> (Where the scores of all participating mages are combined)
If Potency on this first turn is 0 or less, the spell fizzles out and dies.
If Potency is greater than 0 but Luck is less than or equal to 0, the ritual collapses and a random magical will effect anyone near the casting site, with power and area effected being dependent on total potency so far.
On the next turn, the "Head" mage decides whether or not to continue the ritual. If he/she decides to halt the ritual, the spell fizzles out and all essences/magic shards/ items used on the ritual are destroyed and the power is lost.
If the "Head" Mage continues the spell, he may decide to declare that this is the final turn for casting the spell.
In every case where the spell continues, the D6 dice from earlier are rolled. If the total amount of Luck and Potency contributed on a given turn (Dice scores + Stuff Sacrificed) is 0 or less, the spell will collapse (Before deciding on collapse spell effect add on any bonuses that would have been counted to the total stats of the spell.)
Assuming that the spell doesn't collapse, add the total amount of bonuses gained on that turn to the spell's total stats.
(The head mage will have speed reduced to 0 while casting for the purpose of interfering mages, but all other participating mages can join or leave the ritual as they please. (although if this is their first time joining a spell, they must get permission from the "Head" mage.)))
((EDIT: I just read the posts above mine and saw that a similar system was proposed))