The casting is always a collective project; a group is required for the summoning. The location of the ritual is always one surrounded by myth: the tomb of a great warrior-queen, the crashed space ark of ancient progenitors, a Nexus Point through which demons also pour.
Depending on the World-Skein and the Paragon desired, legendary artifacts, musical instruments, magical implements, or sacrifices may also be required for the summoning.
The Paragon summoned may be of a different species, gender, or culture than its summoners expect. Each expresses some essential and critical difference from those who have summoned the Paragon.
More rarely, but often enough, the power of the Paragon invests itself in part or all of the collectivity that summoned it. There may be no "body" for this kind of Paragon; instead a living Company becomes its own champion. This is the most durable kind of Paragon and can endure for centuries.
Many summoners assume that the Paragon will be their natural champion, without a need for the effort to persuade the Paragon that their cause is both just and desirable. Don't make that eternally recurrent mistake. Paragons have no natural affinity for their summoners. They often change side, develop their own allegiances, define their own Great Causes.
Make your case. Hope for the best. Roll 4DF
This spell is of course inspired by Elric, Corum, Hawkmoon and others: the many Eternal Champions that Michael Moorcock has introduced us to over the decades!
*GMs will want to set a specific target based on the storyline and circumstances of their game.