Im going to hate this event

No one has a servants roster that's Lack of Tank, since Mashu is a part of it.

Get yourself a decent Kintoki Berserker support, and build a team around him and you're good to go, since Kintoki gets an initial 80% ATK boost being a Japanese Servant. If he's equipped with a 100% damage boost event CEs, all the better.
Unlike Ibaraki, I've noticed how this Event's Raid Bosses deal abysmal damage, and I've been having a good time destroying the 1,000,000 HP Raid with only Herc, Mashu and Kintoki (Sp who doesn't even have event CE). The odds are stacked in your favor this time, since besides the boss, there's only 1 guy (who should die easily in turn 1 thanks to Kintoki's NP) and you receive a damage boost (Will to Fight) at the start of the boss fight and it lasts for 999 turns.
There's always something to do: look for a better support, enhance that reliable Servant that you've been neglecting, or if you're really out of options, doing the 300k Boss isn't that bad. I heard you can clear the Event just by doing the 300k Boss, but as you rack up your damage points, you'll be rewarded with Event CEs that boost your damage and eventually make it possible to easily do the 1,000,000 or even the 3,000,000 one, and that should be enough for us f2ps.

Maaaaaaaaash
Mash is best budget tank. Mash is one of best NOT budget tanks, even at level cap 60.

The good news about raid events is that you can still farm daily quests and participate. You can snag those XP cards while not having to use resources to continue to raid. I recommend finding that random Benkei, Kojiro, Ushiwakamaru, or Kiyohime you hopefully didn't destroy/use as food and pumping them up if you want to use the extra damage.

Look for Kintoki Berserker, Rider Kintoki, or Waver/Tamamo as supports for Green Gate.

You've got this.

I'm pretty much hate the event. It level is soul crushing for me, especially the raid battle. F2p

wowowow. . .Everybody saying ''I am goin' to hate this hard hitting boss event cos I'm F2P and i have low rarity servants and stuff. . .Guys. . I am a free to play player too.Even ''In-App purchase'' is off in my setting believe it(lol).I Have been playing only for 2 months and I have some wierd luck too .I have 4- SSR servants(Mr.Goldenzerker,Artoria,Tamamo-no-mae-Scathach) , lvl (70,80,80,50). And I don't use them much becos Berserker - farming only due to lack of good def supports in my pocket,Artoria - daily farmer,Tamamo- rarely use with mashu in some bosses.Scathach - low lvl. For now I can easily beat Hp 3,000,000 Green Oni. How? Do i use all my SSRs? Nope. I used Lvl 94 Ushiwakamaru(100%dmg Event CE), a support servant, lvl 70 Mr.Golden(Kelidoscope),Lvl 50 Rider Golden(Dumpling Over flowers CE),lvl 60 Mashu(Pheonix Reversal),and lvl 1 kojirou as CE holder. Ok . . .How do I fight the boss? Simple.Boss is Caster type(strong against Quick cards and Assassins, so Assassins are out of option),So I picked my Grailed Ushiwakamaru(Np 1 btw) since she is ST rider. when battle start i use Mr.Golden's NP gain so with Kalidoscope he is at 100% Np and good to go.and I use Ushi's NP gain up buff. and use some art card to build some NP b4 boss turn.when boss came in i cleared Kojibro using Mr.golden's Burster Brave NP with Ushi's attack buff+ Kintoki's attck buff.And main Trouble for my Ushi is gone.After that I let mr.golden die on purpose.and let Rider Golden come in. And Rider Golden start producing Golden Stars and Ushi hitting lkke a truck with just Normal cards.when Ushi NP is 100%( I can't go further since she is NP1 lol) All attack buff up+ Master Attack buff) Boom! Hit for 400k. and boss won't do any more big damages since Ushi and Rider Golden are Riders. Ah yes i bought Exp Cards with corals for Rider Golden power Lvl. Simple! This is how I am playing!
Your Truthfully
F2P Destrogram xD.

Well This is Proof. ( I screwed up in this one tho. out of turn. Got bad Decks the whole battle) well i managed to reduced him to that Hp from 3000k.