Warcraft III: The Frozen Throne Walkthrough & Game Guide

Mission 5: Gates of the Abyss
Two days later upon the desolate plains of outland, Illidan and  Prince Kael'thas
prepare to assault Magtheridon's dimensional gateways.
Start off the mission by simply defending the attack  of demons that come through
the dimensional gate for three minutes.   You'll have to fight off some diabolists
a and fel stalker/beasts/guards.
In this mission you can build both blood elf and naga units.   I would focus on
building ranged unties with human, and building myrmidons with the naga.    You
will definitely want dragon hawks in this mission,  especially if you intend on
sacking all of the fel orc bases with the Draenei (not necessary).
If you need more farms, or food, I'd build coral beds.   They give you 15 food as
opposed to 5.

Make sure to upgrade your naga units if you choose to use them at the temple of
the tides.

I would also suggest making either sorceress' or  sirens.

Make sure your base is well defended, because you will be going all around the map
to seal the portals.  You can also choose to just move your base elsewhere.  Once
you destroy the orange orc base you can set up your base there and never be
attacked.    Although money is never really an issue in this mission, you can set
up an expansion at the gold mine to the northeast of the first gate.   After you
close each gate the location of the next one is revealed to you.

Tech to castle right away, as you should have a lot of money.  Get lots of dragon
hawks, while making myrmidons and archers if you want.  Upgrade your units. Make
sure to get cloud for dragon hawks.

Head south from your base and you'll see a cut scene about the draenei (buy a town
portal from your arcane vault, just in case you get ambushed.

Optional Quest: Draenei village
-destroy the Orange Fel Orc Base
I'd do this mission just because I think it's easier to maneuver to the different
gateways if the Draenei are distracting. Head to the east from the Draenei
village.   Go into the base, cloud the first group of towers and burrows/farms and
have illidan metamorphosis.  Tornado if you need to.  Flamestrike everything and
you should be fine.   Once all of the unit producing buildings are destroyed
you'll talk to Akama, a Draenei, and complete the optional quest.
--
Head east from here, and you'll find the second gateway.  Here there are some
nether drakes and other demons.  Use your dragon hawks to shackle them and
myrmidons to mop up the ground forces.    Then have illidan step on the circle of
power to seal the third gateway .  yet another onslaught of demons will come.  I
tend to stay further back, near the circle so I have time to shackle before the
air units get there.   The demon force consists of nether drakes, fel beasts, fel
stalkers, voidwalkers, an occasional fel ravager and eredar diabolist, and
infernals.  Once you've survived that for 3 minutes,  that gate will be sealed.

If your gold mine ever runs low, be sure to expand in the gold mine that you
cleared when you did the optional quest (if you did it), in addition to the one
that was cleared after the first dimensional gate was cleared.

You can head over to the third dimensional gate if you wish.   You can also take
out the dark green fel orc base with the draenie to clear yet another gold mine,
it shouldn't be that hard, but you will probably lose some forces, and you can
ignore it totally if you wish ( just go the from the south west path to the third
gateway, to get there band not go through that base.

At the third dimensional gate, there are some bloodfiends and overlords.   They
can't hit air so harass them with  your dragon hawks if you do not want to fight
them. There are also some vile temptresses that have some nasty spells, so take
care of them with your forces.  When you are ready put  illidan on the Dimensional
Nexus.  This gate consists of vile tormentors, bloodfiends, vile temptresses  and
the occasional blood fiend queen of suffering and eredar diabolist.  After 3
minutes of this the gate will close.

Head over to the final Dimensional gate.   Slightly southwest of the purple base
there is  a fountain of health.  Kill the creeps there and then crack open the
cage to get some draenei to add to your group of units.
I highly do not suggest going into the purple base to the north.  It  has a bunch
of red dragons that are spell immune, and therefore can not be aerial shackled.
Just go to the fourth dimensional gate (upper left corner if you didn't realize it
just popping up on your minimap), and defeat the doom guards and diabolists
guarding it, along with the nether drakes.  It will probably be a hard battle but
meta and flamestrike make it pretty easy.

When you are ready put illidan on the final dimensional nexus.  Most of the units
that come out of this dimensional nexus cannot hit air, and there are a few air
units as well that can be shackled so dragon hawks will be a good choice. You'll
also want a LOT of myrmidons because you'll need to tank a lot of damage.   Don't
be afraid to use the mercenary camp right near here if you have money.
Doomguards, infernals, fel beasts, fel stalkers, fel ravagers and maidens of pain
will come out of this one.  This is very difficult and I suggest having almost
full upkeep if you want this to be even remotely easy, although it is not
necessary.     Keep building reinforcements , and getting more mercenaries if
possible.  Once this is sealed off the mission will be completed.