Warframe

It's been a year since Plains of Eidolon are out, and still no guide ? I guess most of you searched on YouTube for tips, but I'm gonna add a guide here as you can do this solo.

First of all, I cannot confirm you have to kill or capture the Teralyst as my achievement is broken (I've killed over 100 of them, counting also the other new eidolons, and it wont unlock, even though the support knows about this issue).

Also, if you go on Cetus at night, you can search for squads trying to kill Eidolons within the bounty lists.

Doing so will put you with randoms and might grant you the achievement, but you might need to be prepared a bit to help at least a little. I'm not here to help you get the achievement this way. I'm here to help you understand the achievement and how to do it on your own, without just being assisted by randoms that do all the work.

######

Ok, so what are the conditions to start going for this achievement (considering you're doing it alone) ?

FIRST : You need to have completed the main lore (up to The War Within) to have your Tenno and it's own weapon. If you don't, this will be nearly impossible alone.

SECOND : On Cetus, you need to find the Quills syndicate. It's somewhere hidden in the NE part of the city (considering the main gate as North).

The syndicate will let you get better weapons for your Tenno, which are mainly required to defeat the Teralyst.
To level up in this syndicate, you need to get Sentient cores, which are dropped by damaging/killing Eidolons. The fastest way to start this syndicate easily is to go on the Plains at night, to try and kill some Eidolon Vomvalysts (100% drop chance for Intact Sentient Cores = Each core is 100 points for the Quills).
Considering you need to reach the 2nd rank (Observer) to build the amp down below, you will need a total of 300 Intact Sentient Cores (by the time you try this achievement, you should have already earned some - 300 Intact Sentient Cores because 5K pts to reach lv 1, 10 Cores as a sacrifice to lv 1, 22k pts to reach lv 2 and 20 Cores as a sacrifice to lv 2). And obviously you'll need some more to get the parts I recommend.
(If you take the Pencha Scaffold by reaching lv1 and the Shwaak Prism by reaching lv2, you'll only need 5k pts to get the last part - Juttni Brace)

THIRD : Let's get to the composition :
- Warframe : I'm gonna explain the best combination for groups, and then you can pick one of these for yourself, but then I'm gonna explain which one I choose for my solo runs.
[TRINITY/PRIME] : Trinity is the most needed frame while fighting eidolons. Not to protect the allies but just for one thing => Healing the lures. (I'll explain this later in the guide).
[RHINO/PRIME or CHROMA/PRIME] : If you know your basics on MMORPGS, you know that you basically need 4 types of players (Healing, DPS, Tank, Crowd Control). Pick one of those two frames to use it as the DPS type. (Explanation for Rhino use later in the guide).
[HARROW] : Here, the priest isn't technically a Tank or a Healer. It's both. Harrow can protect your whole team from the magnetic waves the eidolon sends everytime you destroy one of its members, and he can also buff the team with critical chance/damage/headshot damage with the same power. He's beast !
[OBERON/PRIME] : As Trinity, Oberon can easily heal the lures, but also protect the teammates from dying with another power. I do not recommend him because the other frames are better on their own, but still, he can help you a lot if you take him.

On my own, I bring Rhino, because he can absorb a lot of damage and still be one of the easiest/strongest DPS in the game.

- Weapons : You need to know directly, that TWO THINGS are most important when it comes to achieving a lot of damage on targets like the eidolons. What element is best against him, and the critical damage/chance. Currently, the best weapons to do this so far are the snipers. Long distance, heavy damage, high crits, they are the best. Take the Vectis/Prime, the Vulkar/Wraith, the Rubico they are both good, but the bests are the Lanka and the Rubico Prime (still not tested this one, but the stats shows it's a beast).
The goal here is to get critical chance/damage and radioactive damage. The Lanka needs to be charged to shoot, but it is 100% electrical, which gets radioactive with fire, with insane numbers !

- Tenno weapons (Amps) : You'll also need a decent tenno weapon to help you defeat the Teralyst because his shield can only be damaged with Void damage, which is only provided from the tenno weapons. With the Quills syndicate, you'll need to reach the 2nd rank there to unlock the best parts for your AMP (or at least, the more decent ones, because the last parts are not really that good).
My first (easiest) amp I built was the Shwaak Prism, the Pencha Scaffold and the Juttni Brace. But if you've come to the 3rd rank, I've upgraded (built another in fact) my amp to put the Lohrin Brace which incrases critical/status chances, which is the best Brace in this case.

- Focus : Basically, the more focus points/abilities you'll have unlocked, the best it will be. What you need to focus on (no pun intended) the passive abilities you can unlock on every focus tree, because they can bring buffs to the main focus tree you'll use in fight.
For the focus tree you'll use, they are two schools that are fighting. I use Unairu but other people use Madurai. I found Unairu to be faster to unlock and easier to use, but both are really good.
[UNAIRU] : The perks you need to unlock/upgrade on Unairu are Unairu Wisp (and both passives if you can). To explain : When you use your melee close to the Teralyst feet, it will spawn a special little wisp that you can pick up which will grant you an extra 100% damage during 12 seconds. And you can spam the melee as you wish, but the timer of the wisp doesn't go over 12 seconds.

[MADURAI] : The perks you need to unlock/upgrade on Madurai are Void Strike (and both passives if you can). To explain : When you hide in the void mode, you're charging a counter which once out of the void mode will give you extra damage for the next X shots you're going to do, which applies on both your Amp and your weapons. I'm not a huge fan of this because you need a lot more focus to max this perk, and this takes more time to use/charge than Unairu.

[VAZARIN/NARAMON/ZENURIK] (optionnal) : The passives you need to unlock are Rejuvenating and Enduring Tides for Vazarin, Mind Step for Naramon and Void Siphon and Void Flow for Zenurik. But all of those are optionnal.

Now that you have this basics, you can try to defeat the Teralyst. Obviously all of the things listed above doesn't need to be unlocked to get the achievement, those are only what will help you get the achievement easier. I really recommend doing it with people, but yet, you can try it on your own. I'll try and upload a video of a run I did using these tips.

HOW DOES EIDOLON HUNT WORK ?

First, eidolons only spawn in the Plains of Eidolon at night. The best is to go on the plains just when the night begins because the Eidolon will leave as soon as the day comes. The night lasts 50 minutes, which might look short if you don't master the gear you use. My shortest run for a Teralyst (in group) was 7 minutes. You can check the time on the Plains/Cetus with this site : https://hub.warframestat.us/timer

Once you get in the plains, ready to fight, the first thing you'll try to do is locate the Teralyst. You'll look for a big noise and/or a big blue light emerging from the ground (only for the 20 first seconds of the game). It is best to spawn an archwing as soon as you enter the plains to get faster moving around the map. Also, you can note that the Teralysts will most likely spawn around water areas so try to look for them asap.

Once you located the teralyst, put a marker on him and then go to grineer encampments to try to find, kill and hack Lures, because you'll need to have at least 2 of them with you while fighting.

When you have lures, you need to charge them. To charge a lure, you need to kill Eidolon Vomwalysts (the little creepy monsters that roam at night). To kill these Vomwalysts, you need to take them down with your tenno weapon (Amp). They have two steps, first when they look alive, the second when the look transparent/blue. You need to kill them until they are no more (this tip might look odd, but when you never see them before, it's useful to know how to kill them). You need to kill 3 Vomwalyst to charge 1 Lure. Once the lure is charged, it will change it's color (only the indicator) from Yellow to Blue. If you carry more than one lure at a time, killing 3 vomwalysts might not turn one blue because the vomwalyst souls will go in either of them, so be sure to have both your lures charges by killing 6 vomwalysts. Do this while going back to the Teralyst.

Here the fight begins ! To damage the Teralyst purple shield, you need to shoot him with your Amp. Try to help yourself with your focus skills if you can. Shoot the Teralyst anywhere until you see hiw glowing red (meaning he's vulnerable to your bullets).

When you can use your weapons, shoot at the Eidolon Synovias (Arms and Knees). Do not bother zooming with your sniper to get the little multiplier it offers and kill it as fast as possible. Focus on the same Synovia until it's destroyed. Once the Synovia is destroyed, if you're playing with a Harrow, he should prepare his 4th ability to protect the whole team from the magnetic waves the Teralyst will send. If not, you can protect yourself from the damage by swapping to your tenno, then enter void mode (be invisible). This will prevent any damage you can receive while on your warframe (but this will make you lose all the energy your warframe had/This consequence doesn't happen if Harrow protects you).

Make sure you have Lures close from you while you fight the Teralyst otherwise he will teleport to another place on the map.

If sometimes during the fight he screams and become glowing blue, he called for help from the vomwalysts around. You need to kill them to remove the shield they're giving him.

Rinse and repeat 3 more times to destroy all of his synovias, then prepare for the last part of the fight.

Once all of his synovias are destroyed, he will not emit magnetic waves, but instead he will fall and call for help from the vomwalysts. Kill as much as you can, and then, if he got some shield back, remove it with you amp, otherwise, directly damage him wherever you want (head recommended).

Once he's dead, two things can occur. If you have at least two lures close to you while he dies, his body will be captured, and two lures will explode leaving a bunch of rewards on the ground (Arcanes, Eidolon stuff, etc..). If you don't have at least two lures, his body will fall on the ground and he will be considered dead, not giving you rewards.

Normally, at this point, the achievement should pop. If not, please feel free to post a comment down below to let me know.


Now I'm gonna add some other few tips and my full equipment for solo runs :

TIPS :
[ARCHWING] : Think to bring archwing capsules with you to get faster at the beginning of the fight. Amesha and Itzal are the best to use, but Itzal is by far the fastest of them.
[SECONDARY] : You can bring a secondary weapon with you, but a few can actually be efficient. The most efficient one is Lato Vandal, but if you appear to have this weapon, you've probably already killed a lot of Eidolons before, due to the rarity of the weapon.
[MELEE] : Melee will be uneffective against this situation, BUT it appears that I always bring a Sarpa with me, with the Shattering Impact mod on it, because it can down the armor of the Eidolon. To make it clear = Each Sharpa shot is 5 shrapnels. Shattering Impact removes 6 armor pts per hit. Which is 30 armor removed by shot. The Teralyst has 200 armor, which can be removed in 7 shots. BUT you do not want to remove its whole armor, because if you do so, Radiation will not be the best damaging element anymore. (it's based on how health/armor resistances work, and nothing beats radiation on armor in this case).
[RIVENS] : If you can get a Riven mod for your sniper, you will achieve a lot more damage, thus making the fight even shorter. But, if you consider buying one from other players, I just want to remind you that Rubico rivens sell for around 2000 platinum and Lanka ones for 1500 platinum...so...best luck ^^
[ARCANES] : The best arcane so far for this...doesn't exist. But, I use maxed Guardian and Barrier Arcanes on my Rhino. You might tell me that how could you have arcanes if Eidolons drop them. Well, back in the days, the arcanes came from Raids (which doesn't exists anymore...RIP raids), plus you can also buy them from other people. Also, one of the cheapest arcanes that can help you doing this (even more if you're running solo) is the Arcane Zero (which will grant you resistance against Magnetism, helpful to counter the waves from the defeated Teralyst) If you do so, you will try and look to equip at least and Arcane lvl 3 and another lvl 2 to reach 100% protection against magnetism.
[VIRTUOS/MAGUS (arcanes for Tenno/Amp] : If you can have some of these arcanes, it will be great for you and help you a lot while fighting the Teralyst. The Magus arcanes are here to help your Tenno. I use one Magus Vigor (which gives me more health for my Tenno) and Magus Husk (which grants me some more armor) but you can use two Vigor if you want. Those arcanes are really cheap so mind trying them.
For the Virtuos (Amp arcane), you'll look for Virtuos Strike or Virtuos Fury (I've found Fury to be a bit more efficient with my Amp, but both almost buffs the same amount of damage).
[GEARS] : With the archwing launcher, I would also recommend you take some energy capsules (restores) to help you refill when you take magnetic waves (which emptied your energy) and obviously some ammo caps if you're not that good at aiming efficiently.

And now my own gear I use for my solo runs with some explanations : Spoiler there because I've added a lot of pictures of my gear


I hope this full guide will help you understanding in details how to get this achievement with a long preparation (Who said Warframe was easy ?) My goal was to try my best to let you know about ANYTHING you could do to get this one done the best way possible.
Hope you like it, and if you need anything more, let me know in the comments !
(P.S. I'll try and add more visuals to the solution to make things clearer, and try to add a gameplay vid of my own try)