Free quest Tathagata help

Drake is awesome because she can help provide the party attack and NP boost and she can fire her NP at third wave given she has more than half NP charge. The next best rider support is Santa Alter as she is guaranteed to clear the caster mobs in third wave with her NP. Try Mash/George + Heracles + Santa Alter. If you need to clear consistently, trade some damage CE over Nightingale CE and put it to Herc. I only have Santa Alter so I hope you can find Drake supports.

Alternatively, you can try George + Heracles + support Waver so Herc can fire his NP along with Waver's buff.

I've got a Drake and a free spot in my friend list. Post your code, I'll add you

For Tathagata, I'm running the following team, with Nightingale CE Equipped (except for Bride) with
Santa Alter lv 80 (6/6/6)
Nero Bride lv 90 (10/10/10)
Support Rama or Okita. I prefer Rama tho
Backline: Medusa, Euryale, Caesar.
I always cleared it without major problems, Bride can be replaced with another support servant. I have Waver, but I don't want to use him at the moment. 1st and 2nd wave, just build NP and make stars, and on 3rd Wave, it depends on cards. I always try to get rid of Lamia first, and Crits with buffed Rama in the end.

For me works:
JAlter 98lv. 10/7/10 - Maiden Leading Chaldea (Limit Broken)
Waver 90lv. 4/8/10 - Ox - Demon King
Hans Andersen 65lv. 6/6/6 - BLANK
Heracles 80lv. 1/1/1 - Limited Zero/Over
Any support with Nightingale CE
Cu Chulainn 90lv. 8/10/10 - Ox -Demon King

I just going for arts chains and using Hans NP on 200% or 300% overcharge to keep my party at safe hp. Rarely i need to use support servant, usually i end on Herc becouse Hans dying.

(Yeah i know i came to event late so i don't have my own Nightingale CE yet)

I've been running Mordred - Georgios - Support Drake for clearing, all with Nightingale CE (Though I waste 20% drop chance)
The first turn I use both Mordred's 3rd skill for 30% NP and Drake's NP, then I just charge the NP while also clearing as fast as I can, then the last wave, I pretty much get rid of casters with NPs and just kill LAlter with busters chains and crits.

How about swapping in Mash or David when Lalter's NP is imminent so your main damage dealer (I'm guessing it's Cu Alter) doesn't die? Having Cu use his dodge before her NP is also a good idea.
Can't help but feel weird about you having Herc and Cu Alter on the same team (and same front, too!), though. Maybe switch Herc with a support or stop choosing Cu, let Herc handles his role, and use a good Rider support like Drake.

My advice:
1. Re-arrange your team position. Your placement is pretty much asking for both your damager to be killed. It would be better if your placement is: 2 support and 1 damager in front, and another 2 support and a backup damager in backline.
2. Bring an AoE Rider. The basic strategy for this one is basically kill the snakes first before LAlter as the snakes can heal. You don't really have to bring Drake as Medusa is enough to kill the snakes as long as she is leveled properly.

I used:
Frontline: Leonidas, Medusa, Waver
Backline: Mordred, Shakespear, Mashu

Tbh Waver isn't really needed, Hans is enough. I simply used Medusa NP in the 3rd wave to kill off the snakes and then swap her for Mordred. My Mordred have kaleidoscope for her ce so she can fire her NP right away. Shakespear is there in case if Hans or Leonidas is dead so Mordred can still more buff from someone else. My Mordred killed LAlter in 2 turns only lol.

I hope I am not late in answering this, btw I am a f2p and a very new player in FGO, my front line contains Cu Lancer, Rider Ushiwakamaru, and Okita, and support line contains Mash, Medusa and Hercules along with default Uniform for your Avatar. What you need to do is clear the first 2 waves without using the NP of any of your characters, and when you are in the 3rd wave first attack the odd looking caster and try to kill her with your rider and if she doesn't die then no worries coz she will automatically use her healing skill, then in the next turn Use first 2 of Okita's skill at once along with your command attack boost now use try to chain her Buster quick and her NP(This almost 95% of the time single shot Lancer Alter) after that all you have do is kill the last remaining caster.

On a side note if your rider dies during the 3rd wave then have mash activate her invincible and taunt skill so that she can distract the enemies, andalways save up Okitas evade skill in case you mess up killing lancer alter and use it to avoid her NP.
Hope this helps, btw what to do with the extra
Lotus after purchasing all the items??