Edit Narshe Esper battle

What about reduce the speed of Rider, instead of the whole armies?

For that, there's 2 things you can do.

1. The Rider's script is at CC/CEC5. He runs back and forth, and has 2 pauses of 16 frames. You can change CC/CECB and CC/CECF from "E0 04" to "E0 08" to double the length of the pauses. 
2. Your second option is to slow down his actual running speed, which would mean changing CC/CEC7 from "C3" (Fast) to "C2" (Normal) or "C1" (Slow). Note that the Slowest (C0) and Fastest (C4) values are really only for the camera. When used on NPCs or Characters, it looks really weird.