Darkness is cast first, then rain:
Mordor won't get LD.
Rain cast first, then darkness:
Mordor won't get LD. (only units made after rain is used can get LD)
Rain cast first, then opponent rain:
Both no LD
My darkness is cast first, then his:
Both get LD
Rain cast first, then cloud break:
Still no LD, but armor and slow debuff is applied.
Darkness cast first, then cloudbreak:
Darkness LD remains, but armor and slow debuff applied.
