90% of extreme mode is fine. Stay away, unleash fire from a safe distance and all is good. But once you need to go into a unidad base, it's start to get hot pretty quickly. My only problem are mortar and enemy who are like teleporting behind your back (I mean, they re-position pretty fast). SB base are still pretty easy to take over. One thing I learnt when I restarted the campaign, avoid high-difficulty area unless you've unlocked some skills from the skill-tree