Do you mean to control the ennemy unit ? (Ennemy control Glitch) https://fireemblem.fandom.com/wiki/Enemy_control_glitch#:~:text=Advertisement-,Fire%20Emblem%3A%20The%20Blazing%20Blade%20Glitch,control%20the%20enemy%2FNPC%20units.
Or to manipulate the RNG/Luck (ennemy miss, level up, critcal hit,...) ? https://forums.serenesforest.net/index.php?/topic/28299-how-to-manipulate-the-rng/
Both are used in the speedrun and very usefull. It's not easy to understand how the rng works at first but then it will be cool to use it eh eh. I will send you a PM.
I'm DXSteveX, you can telle me Steve ^_^ The first time i have watch a FE speed run that was Path of Radiance with RushinAssassin. I just say.... Yeah that's very cool to watch...
And after i have watch Bertin who run FE8... that was so nice and sick run... i have start to run without rng manipulation.
The first FE i have play is FE3 on Super Famicom when i was a little boy but japanese was so hard for me, i don't beat this game... ^^
My favotite FE is 8 and 13. I love 6,7,10 too.
I love another game too like : Mega Man, Street Fighter, Touhou, Skyrim, Terranigma...