When Phantom Steed enters the battlefield, its first ability triggers, exiling Abdel Adrian until Phantom Steed leaves the battlefield.
Abdel Adrian leaves the battlefield, ending its effect, causing Detention Sphere to return from exile to the battlefield.
When Detention Sphere enters the battlefield, its first ability triggers, exiling Phantom Steed.
Phantom Steed leaves the battlefield, ending its effect, causing Abdel Adrian to return from exile to the battlefield.
When Abdel Adrian enters the battlefield, it triggers, exiling Detention Sphere and any number of other nonland permanents you control until Abdel Adrian leaves the battlefield and creating at least one 1/1 Soldier creature token.
When Detention Sphere leaves the battlefield, its second ability triggers, returning Phantom Steed to the battlefield from exile.
Repeat from step 2.
This dazzling loop centers on an infinite dance between Abdel Adrian, Gorion's Ward and Phantom Steed, using Detention Sphere as the pivot that constantly breaks and restarts their mutual exile. Each time Phantom Steed enters, it whisks away Abdel Adrian, which in turn causes Detention Sphere to return to the battlefield and immediately imprison the Steed. When the Steed departs, Abdel Adrian rushes back to the field, creating a cascade of Soldier tokens while exiling Detention Sphere all over again to restart the cycle. Because Abdel Adrian's entry trigger can also swallow up any other nonland permanents you control along the way, this rhythmic bounce generates an endless storm of entry and leave-the-battlefield triggers alongside infinite tokens.