Examples of Magic Cards that use rule 115.2c
An example of this (very rare) special action would be paying {U} to prevent the delayed trigger from Quenchable Fire.

Quenchable Fire {3}{R}
Sorcery
Quenchable Fire deals 3 damage to target player or planeswalker. It deals an additional 3 damage to that player or planeswalker at the beginning of your next upkeep step unless that player or that planeswalker’s controller pays {U} before that step.

There are three other cards with a similar template that also use 115.2c: Glass Asp, Nafs Asp, and Sabertooth Cobra.
The Licids from Tempest block also use 115.2c to enable you to end a continuous effect:

Calming Licid {2}{W}
Creature — Licid
{W}, {T}: Calming Licid loses this ability and becomes an Aura enchantment with enchant creature. Attach it to target creature. You may pay {W} to end this effect.
Enchanted creature can’t attack.