Ok from what you have (and lets ignore free to play character), you clearly lack a earth element (for shielding).
Diona+Mona+Fischl+Diluc should work pretty well. (you can switch mona out for barbara is you need heals)
Trow down mona tank skill, switch on diona and trow her aoe (everything will frezze), then bird with Fischl and finish off with Diluc.
If you have Sucrose, you can use her with any of those 3 characters in setup (but you need to have at least C1 on her or CD is to looong).
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Anyway some news:
Zhongli's passive - When crafting spear type weapon, return 15% of the used mining material. LOOOOOOOOOOOOOOOOOOL
Also seems like rewards go up by world lvl (screen is from other servers where event is up):
Much better than 25 i say. Its unknown wich world lvl this guy is tho.