The effect to change the Level and halve the ATK/DEF of this card is a Trigger Effect that activates at the end of the Damage Step.
If "Max Warrior" has its Level and ATK/DEF changed by its own effect and your next Standby Phase is skipped, the Level and ATK/DEF of "Max Warrior" will return to normal at the start of Main Phase 1.
If you use the effect of "Assault Armor" to let "Max Warrior" attack twice and destroy two monsters, its Level will be 2 and its original ATK/DEF will be ¼ of their printed value.
You choose when during your Standby Phase to return the Level of "Max Warrior" and original ATK/DEF to normal. It does not start a Chain.
The halved ATK/DEF is considered the original ATK/DEF while the effect of "Max Warrior" is being applied.