I'll start with some that come to my mind right now, which is mostly shakarn promethean, that's the last combination i recently used. Also this is for singleplayer
1. Phoenix walker with themselves. No mod is already good, although mods that increase damage is always welcome, because the walker don't have abundant of options for offensive mods.
2. Phoenix walker with any units, or unit with mod that can cause hazard, or any unit with pryx absorb mod
3. Shakarn Tactician with any units with either long range abilities or area damage abilities or both. Tactician + Sonokarn or Tactician + Refractor is a good example, these
are good even without any mod as well
4. Shakarn Tactician + Phoenix Walker with Teleport mod (i think the mod's name is orbital recall system), better if the phoenix walker is a hero riding it, add sono-fin mod to that hero for even better combination. You have a hero which is literally a tactician with the combat capability of a phoenix walker. Pair the heroes with other phoenix walkers, or sonokarns or refractors or any combination of these for cataclysmic long range Area damage. Often your enemies doesn't even have a chance to even attack even once before they are obliterated. The only Mods needed are damage boosting mods, although for those sonokarns, the impaired mods, disintegrating laser and shield reducer laser mods are great. The only downside is this is for late game, unless you can get them faster and is lucky (by lucky i mean you find at least 2-4 cosmite mine near you). Can be paired with strategic ops incinerate strike for even more destructive effects.
I like a combinations of 2 sonokarns, 1 hero version phoenix walker with sono fin, 1 tactician, 1 aegis tank, 1 phoenix walker per army or stack. Just need 2 or 3 of this stacks or ideally 4 for any offensive or defensive goals. The walkers are for repelling close or melee combatants who manage to get close, if they can get close before getting obliterated by the two sonokarns, that's per army, because it's generally recommended to use 3 or 4 armies marching adjacent to each others, so, 6 or 8 sonokarns with those other units supporting them are massively overkill. Tacticians are mainly for refreshing the sonokarns and the walkers if enemy units manage to get close, or enemy units are very agile if attacked with ranged weapons, the walkers can jump in to melee them, refresh as needed, useful for defeating those voidbringer leviathans, before they use their call of terror area attack
5. Sonokarn + Aegis tank. Their shields stacks, giving you massive shield bonus and thermal resistance
6. Hero version phoenix walker, with secondary weapons that are sonic type, with impaired mods or other great sonic mods, like reverb one, pair these heroes with either tacticians or other hero like that, and you can rain area damage and area sonic debuffs. Press the advantage ability is the key here, beside the obvious area attack abilities. Tacticians can also equip orbital systems to allow them to teleport, cavitation module (reverb) is also decent to finish the reverb stacks
7. Amazon harrier with phoenix bomb launcher, regeneration mod, any damage mod, or two regeneration mods available to amazon also stacks. Pair it with themselves, this is probably one of my most favorite combinations. The only downside is they have massive cosmite cost. Fast, flying, have range 9 area damage, regeneration, they can defeat forces larger and more powerful than themselves if played correctly. The fast and flying also apply in strategic map, meaning you can raid enemy backline strategic positions then retreat if needed. Even better if happen to finds one or more landmarks that give boost to Heavy non elite units. Paired with amazon doctrines, you can have 70 to almost 90 HP units which can regenerate 20 HP per turn, about 2-5 shield and few armor if i remember correctly in addition to the facts above.
