The way to do this is to add the starter battle sprite to the corresponding class. It would be like this:
Striker: Drakon with Firebolt.
Recon: Maskeraith with Caustic Quills.
Guardian: Seraphynx with Ray of Light.

You can't bring your own sprite into Lockdown, just like the shield. They will be level 1, not evolved. When you use your shield, the battle sprite will have their defensive power on your shield. It would be like this:

Striker: Drakon makes the Striker Shield deal a little damage from its Flame Barrier move when you run through or into someone.
Recon: Maskeraith gives the recon shield a little more defensive power from Shadow Cloak.
Guardian: Seraphynx will give the Guardian Shield more shield health and maybe make it larger(?)

"Those who cherish friendship make the most of their adventuring!"
-Pery