High Watchtower is the fourth stage in Quarantine Isles.
Nothing spawns out of the enemy base at first. After a short while, Galactic Overseer Nyandam appears, along with Those Guys, B.B.Bunny and Squire Rel serving as peons. Awhile after, Bore will be spawned, with Razorback following soon after.
Despite Nyandam being the boss, the main threats here are the Bores, especially Razorback. Make sure of bringing units to slow or freeze them. Also, try to kill the red bore quickly, or else you'll have to fight Bore and Razorback together, making the battle nearly impossible. Bombercat and iCat are almost essential for this stage. Cat Machine is also highly recommended. If you have these 3 cats, fill the rest of the slots with 2-4 meatshields and several high damage attackers (A. Bahamut is good for several hits on Galactic Overseer Nyandam, and Lufalan Pasalan is good for damaging the bores).
Note: The stage can be beat pretty easily before the Razorback has a chance to spawn
Strategy 2 (Cheese, No Uber)
This really relies on your cats level, the higher the level the faster you will do the level.
In this strategy you will beat the stage before Razorback has a chance to spawn.
The cats you will need are:
4 meatshields, a strong and spammable AOE cat like cyborg or crazed ufo (I used Jizo but I am pretty sure you can beat it with the ones I have suggested), hypermaxed castaway, hypermaxed elemental dulist, hyper maxed can can, Icat, a fast cat or uber like lion cat.
First, wait and stall maybe use a few manic mohawks and upgrade the worker cat but, just wait until the Bore is spawn. When it is spawned spam everything you will build a large stack and kill the Bore along with Galactic Overseer Nyandam. Your Can Can stack should deal about 150,000 to 200,000 damage every hit which should finish the base in seconds.