exorcist89
Platinian
You Need To Clear Stage X-25 and X-50 Without The Mod Or You Will Get "Stage Failed". Without the mod here means the "Auto Clear Wave Menu"
If you get 'Stage Failed', that means your PEN / ACU is not enough. Upgrade your PEN / ACU to 70% of the required, then you can proceed to breakthrough.
Lets say Stage 64-25 required PEN 204.8K, ACU 168.4K, you need 70%(to play safe) of that required which is PEN 143.36k, ACU 117.88K.