In addition to new enemies, consider subscribing to some map mods to mix up terrain generation and introduce some extra challenge to the campaign. Instead of raising the difficulty with super-hard monsters there are quite enough of those in the game alreadythe mod focuses on giving the aliens a greater range of loadouts and behaviours. To install, simply follow the link to the Workshop page and click the green 'subscribe' button. If you're looking to supplement your Long War 2 campaign, they should be a good bet.
Having said that, I've been playing with all these mods on alongside The Long War 2 and haven't experienced any problems. There's always a chance that conflicts could cause problems, so save regularly. As we're loading a bunch of criss-crossing mods at the same time, normal caveats apply. TLW2 is a total overhaul that affects almost all of XCOM 2's systems, which ought to make it hard to mod without causing conflicts. The Long War 2 is greatbut the modding community can make anything better.
