Over the course of a playthrough, what determines the strength and quantity of the alien units you fase on missions? For example, do the aliens grow stronger:
- continuously over time?
- at specific points in time (e.g. end of each month)?
- after each mission?
- as XCOM's squad ranks up?
- as XCOM's tech advances?
- as more regions are contacted?
A few implications of this are:
- If I skip a mission, am I letting the aliens grow stronger while I miss out on resources, or do both sides stagnate?
- Will pushing XCOM's tech forward only cause the aliens to advance as well?
- If wait to start a mission (e.g. a facility assault), do I risk it getting suddenly harder after a certain event (e.g. the end-of-month status report)?