This guide covers what's good and what's not for units and skills. Also tells you how to beat Zone One on insane so if you want to figure things out yourself then SPOILER ALERT.
Random Tips Edit
Stack 40+ zava detectors and aries/lightbringers drop VERY COMMON. FOR ARIES YOU NEED AT LEAST SCORE OF 2000 FOR FION DRONES.
Lowest level that drops all rare units is Tesire.
100% neg resistance - for Zone One boss insane you only need the front of your base 100% neg resistant against the base. You can get this with 4 neg voiders + 3 infinite fortresses (which themselves can be upgraded to have negative resistance) or 5 neg voiders with defensive walls/un-upgraded fortresses. You only need 100% resistance, upgrading beyond that is waste of gold.
In general for max damage, number of chargors = number of attack units. Too lazy to write the formula for this but I've taken high school meth class so trust.
This section pertains to units you can unlock with gold.
THE MUST HAVES (if your base doesn't have these then your base sucks):
Nyon Exist - for unknown reasons this is the only unit that prefers to focus bosses over their minions (most of the time). Your only hope to beating Villalobos. Targetting speed upgrade increases FIRING RATE - must have! EXP gain appears to be the same for every enemy they kill so it's easiest to lvl them up on early levels with no other towers taking kills.
Chargors - Shoots little balls that boost firing rate of friendly units. Can boost other chargors. Cannot have range boosted. Damage increase upgrade MUST HAVE and should be maxed. Health upgrade useless. Just purchase level 1 upgrade on each chargor. That saves you money because upgrades get more expensive each level and it should be good enough; you can always purchase more if you want.
Tech center - get zava detector and max out gold gen ASAP it's gonna be worth in long run.
THE GOOD TO HAVES (only cuz they help you beat Zone One insane):
Vira healer - one of your very limited options for healing your units. Max healing efficiency - everything else sucks. You'll need 4 of these for Zone One insane so might as well upgrade them early.
Neg voider - you'll need 4/5 of these for Zone One insane (depending on if you have three infinite fortresses). Upgrade Team Resistance so front of your base is 100% neg resistant. Other upgrades useless.
THE GARBAGE YOU DON'T NEED:
Everything else that I didn't mention. Either because they suck so bad they barely work (looking at you vira savior), or cuz they are shit for damage.
WHY AEGIS/TITAN BARRIER SUCKS: It doesn't have Healing Amplifier upgrade so you won't be able to heal it fast enough in Zone One insane against Villalobos. Use defensive walls and infinite fortresses instead. Also doesnt protect as much of your base. If you have vira ultimas then this is outclassed by ZAC Assimilator which is just as tanky.
This section pertains to units you can only get as drops, but they are pretty easy to find.
THE MUST HAVES:
Defensive Wall: Max Healing Amplifier. Other upgrades aren't important, you'll need the gold for chargors.
Infinite Fortress: Max healing amplifier and neg resistance.
Santum Beacon: You'll need as many as possible for zone one insane (max 8). Just max sancrify for extra healing.
Arcane wrath: the idea is that if you only have a small space to block off you can use this which also shoots bullets for extra dmg. Why it sucks? Shitty dmg, too small, no healing amplifier, not enough health.
Tesla - dmg sucks compared to Nyon Exist. Doesn't focus boss. Very expensive to upgrade use your gold for something else.
Ultra Rare Units Edit
They don't focus on zone one boss so for that purpose these are all useless.
Healing wave: don't have to max it if you want to save money, as the healing is super boosted by healing amplifier on walls/fortresses. Just level enough so that you can fully heal them when they are low.
Guardian Orb/Decoy: you'll need these to survive zone one insane. Decoy buys you precious seconds to heal walls/fortresses against boss.
EMP: Buys you time to heal up against bosses or a few extra seconds when they rage. No boss should rage though if you use the base suggested later on this page.
GOOD TO HAVE:
Oblivion: Use it to buy your towers time to heal. Will also help against large groups of enemies in Zone One. Very expensive to upgrade, shouldn't be a priority.
Aim here: Sometimes works...
Taunt: lets you farm better
Everything I didn't mention. Either shit dmg or barely works (literally).
Zone One Insane Edit
You don't need super rare units to accomplish this.
You must only use Nyon Exist for offense cuz they are the only tower that wont waste time hitting the minions.
THE FREAKIN OBVIOUS: Healing wave when necessary. Guardian orb gets obliterated but use it whenever it's up. Decoy, Oblivion and EMP when you need extra time to heal.
Chargor: dmg amplifier fully maxed.
Nyon Exist: Targetting speed maxed. ALL NEED TO BE LVL 7.
Healers: Healing efficiency maxed.
Walls/fortresses: Healing amplifier maxed.
Neg voiders: however much negative resistance upgrade to get front of your base to 100% neg resistance.
Use this base 'nuff said. Zone One insane GG EASY.
14 chargors, 13 nyon exist, 4 vira healers, 8 sanctum beacons, 3 fortresses, 8 walls.If you are using 5 neg voiders then take out a chargor