Baaaaam! The first time when I did the Plague mission, thought I was doing it wrong. It's pretty buggy if you decided to do anything else other than letting your units being food for the oncoming Epsilon armada.
Anyways, what's with the spike in difficulty for Soviet between the last Allied mission and the last Soviet mission? I did finish the last Allied mission on easy mode because I could counter any land units with massive pillbox spam on the slope, alongside with mirage tanks scattered, while capturing the nearby Epsilon base and building lots of patriot missiles to counter starflares. But for last Soviet mission, even on easy mode, the above happens and Epsilon sends in the irritable graveller devices and spamming floating disks... It's kind of impossible to counter that amount of enemy forces when your power is down (stupid starflares...)
Anyway a really rough guide for all Allied missions (since different mission guides are scattered around the thread), this is on easy mode (for casual gamers like me.)
Allied 1 "Dead Gardens": Tanya to walk counter-clockwise near to Epsilon base. Get Tanya to veteran, eliminate threats one by one, even Seraphs. To destroy the Psychic Dominator, use the slaves obtained from slave miners as cannon fodder, destroy it and free the Allied and Soviet base. The rest is easy.
Allied 2 "Curse": Issue all units to the west-most area, then move north till you see the Epsilon base. Power down the base, then destroy everything one by one.
Allied 3 "Paranoiac": Easy way out, use navy seals to get the crate from the truck near a narrow valley. Get stealth for both seals (keep resetting till you get it) and you basically cheat through the mission! Hard way... build a strong force and clear the map slowly, but not too slowly. Eliminate the Epsilon base with the Psychic Dominator (except the Psychic Dominator itself) Until one point, you'll see an airfield with some starflares. Capture it, and use it wisely...
Allied 4 "Fire and Water": Clear Epsilon navy nearby. Take a Reveal Crate after destroying the Epsilon Radar southwest of the initial map. Destroy the Time Machine afterwards with whole map revealed to you. Clear the rest afterwards.
Allied 5 "Plague": Let your initial forces get slaughtered, kidnapped by UFOs, etc. Build up your base afterwards with a new MCV given to you, and build up a decent force and kill the rest of the Epsilon army.
Allied 6 "Iron Curtain": Fortify the initial German base with some Prism Towers, tanks etc. Also watch out for another opening east of the map where its filled with trees. Have mirage tanks stationed there. After bridge is repaired by enemy forces, clear it slowly. Also to get more credits, send some engineers to west of the map, where an unfortified Epsilon harvesting base is positioned at, capture it and build another force there?
Allied 7 "Chrono Storm": Position IFVs after chronosphere'd at south of the walls. Garrison your bunkers ASAP and build up mirage tanks near the bunkers. Also build some defenses with patriot missiles and prism towers near the south. IFVs must not die early in the game, otherwise massive Discs will fly towards your base unharmed. Use Chrono Legionares to take out the nuclear reactors below to power down Epsilon-Soviet base. Build up chronosphere and either slowly send the apocalypse tank to the water or send in troops to destroy the base defenses around kremlin.
Allied 8 "Devoted": Send the seals eastwards, killing troops and getting crate from the truck. If you get stealth, lucky you, rendezvous there. Otherwise, navigate your way, watching out for sentry guns and tesla coils. Afterwards, direct seals and transport to the southwest area, again watching out for terror drones and base defenses. Upon there, you'll receive a spy and 5 enforcers. use enforcers to take down sentry guns (enforcers outrange sentry guns by a little... so gotta micromanage a bit), send in spy to tesla reactor, send engineers to the soviet airfield. Send MIGs to destroy the barrel near the psychic amplifier.
Allied 9 "Scarlet Twilight": Destroy Epsilon navy and surrounding structures above the cliff before your reinforcements arrive. Use killer whale to keep a lookout of shadow tanks near the landing spots (2 landing spot, you can choose either, but choose the bottom one) Tech up Allied base asap, building pillbox near cliff to counter, keep apocalypse tank alive, while using your veteran ships to blow up railgun towers etc nearby. capture nearby Epsilon base asap. Tech up chronosphere and send in an armada of tanks in between near the Mental Omega while defending from the crazy horde of units. If you didn't use Soviet MCV, keep it in transport... Destroy Mental Omega and defend against the last wave of units!!