Sold in special packs together with another random power disc
yes
Merlin's Summon is an Ability Disc which, when placed under a Figure on the Disney Infinity Base, provides increased pick up range for Sparks. The disc is exclusive to some retailers (e.g. Toys"R"Us).
In some combinations with a second Ability Disc, a third Ability may be provided.
The disc was released exclusively at Toys "R" Us on April 13th, 2014.[1]