Fiends and garg don't go well together. They might if you don't autocast web and tell the gargs to attack air.
I prefer the Fiend + Abom + Banshees combo. AMS every unit you have (you can coil them anyway, and bury fiends), and possess any tauren/knight/bear/abom they have. Once you're sure they don't have any tier 3, activate curse.
This works pretty well in both RoC and TFT, and against those who don't use priests (few, but even if they have priests, you can still win), and those who don't use spirit walkers (disenchant, but most Orcs underestimate spirit walkers).
AMS is vital, esp to you heroes. You DON'T want to get stormbolted, then flamestriked and blizzarded at the same time, nor do you want to get entangled and then shadow-striked over and over again.
You can add necros if you've got the resources, and in TFT always have a minimum of 2 statues, but don't exceed 4.
Research unholy armor, and creature attack. Priority on abom defense (they're the meat), and fiend offense (they're the damagers). You can also throw in a wyrm of two when you're ready to hit high upkeep.
You can use ghouls before getting aboms, but don't stick to ghouls for too long. Use ritual and pact on them liberally when you've got aboms coming.
