go COOP , it helps a lot. like a lot.
for the two samurai Challenge 3 , apparently there is a time consuming but relaxing way to beat it and get 5050 points.
disable timer , lightning , and respawn of boss. It takes about 10-15 mins but yeah, i did this with friends, though there was two healer in team.
At max difficulty, it took me 3 bursts to take the Maguu Kenkis down. Though in my case, it's because I'm running an R1 pines with a more balanced stat. For
si kutu rayau, the number of burst needed to ohko the samurais should remain the same.
I also ran a cryo resonance + battery for myself while my friend used NG to battery the kind Zhongli who helped us. Still, we managed to complete it within its the time limit.
If kutu is around though, I might have to switch characters cause I don't think we can have 2 Eulas around and my main DPSes only comprise of Ganyu and Eula

, and we'll have to do it 2 by 2 too LOL.
Ganyu is massively "nerfed" in this event, particularly with the Maguu Kenkis. I think she fares well against Geovishap and Oceanid but the time limit severely hampers her usefulness. Technically, if you just wanna get all the moras and freemogems available for the event, you just need get 4.2k - 4.5k average for each challenge. Still... sometimes it's always fun to push your beloved waifus/husbandos to the limits and see what they can accomplish actually.
For Maguu Kenkis, you wanna start off by going for the anemo samurai, as the cryo dude will come to you regardless. In a coordinated/co-op setting, it is crucial that your team hugs the anemo samurai so you bunch the two up together. Especially on max difficulty, you have to time your attacks so you can take the two down together. Failure to do so will result in one maguu kenki reviving and setting you back to square 1. If anyone else starts to aggro the cryo samurai and he starts going further away from the anemo one, that person needs to lead it back to the team.
Team comp wise, I think you'll have to run a shield bot at max difficulty. All the videos on YouTube showing people getting through the challenge with ease usually involves a Zhongli and Eula. So Zhongli is a must-have. And I speak from last night's experience as well. Alternatively, you can run a superconduct team which lowers the mobs' defense and allows someone like Eula to shred through them easily. But I personally prefer Cryo Resonance better.
If you're not running cryo resonance, then I guess the other alternative is to go for a Benett for the heals, or run a Fischl for the superconduct like I mentioned earlier. If your other teammate is doing a good job recharging whoever the C2 ZL is in your team, and that ZL player is doing a good job spamming and keeping the shields going, you shouldn't need any heals to begin with.
Eula is a godsent for high-level challenges like this. The issue with these mobs is they're hyperbuffed in defensive stats. Having that raw burst really helps.
On another note, I really love such events, as it really gets talks about meta going. inb4 someone says there is no meta for gacha games. You could say anyone gets the job done, but at the highest difficulty, you require a very specific team comp or characters to get through it with ease. I.e. Ningguang is highly demanded in this challenge because most people have her instead of Albedo, and she does a great job allowing ZL to battery off her. Meanwhile, someone like Ganyu who is usually topping the DPS charts is playing a more supportive role because in most cases, she won't deal enough damage with her charged shots to take down enemy bosses within the time limit.
I've also seen very underrated characters like Beidou, Fischl and Lisa being used , Beidou especially since her E allows to defend and counterattack simultaneously. Anemo characters are a little obsolete in this event sadly, but maybe that will change in the next few days. But it's always nice to see how the event makes way for "lesser-valued" characters. Again meta stands most effective tactic available, and not who does crazy damage and nothing else. A Bennett won't do a good job being a Geo battery to Zhongli as opposed to Ningguang, so don't let anyone tell you to "just play what you want" at max difficulty

Fuhh, finally got it done in solo mode without Eula at 6850pt.
I went for quick-swap team comp and taking advantage of the iframes instead. Burst iframe + Zhongli + Geo Resonance + Bennet Heal + Moonpie Defense Food buffs + awful dodge skill. Can't properly dodge anymore even since the existence of Zhongli so had to disable 'Increase damage taken after switching character' debuff.