Genshin Impact - Yelan's Ascension Materials Farming Guide

gamespot.com:

Yelan, the five-star hydro bow user, was made available in Genshin Impact's 2.7 update. With a unique dice theme, Yelan's abilities scale on HP. Her kit, especially her burst, can buff your active player on the field. She suits the sub-DPS hydro applicator role well and brings benefits to a group with different element types.

Like other new characters, she's gated behind the latest content. While three out of the four materials for ascension (Varunda Lazurite, Starconch, and Recruit's Insignia) can be found as soon as you unlock Liyue, the final Runic Fang can only be found in The Chasm.

You can find a limited amount of Varunada Lazurite in Souvenir Shops. The following normal boss fights also drop «hydro shards:» Hydro Hypostasis, Rhodeia of Loch, and Primo Geovishap (if infused with hydro). The weekly bosses that drop Varunada Lazurite are Stormterror, Azhdaha, and Childe.

This material can be found on beaches in Liyue. Guyun Stone Forest's beaches have quite a few, as well as Yaoguang Shoal. Check out Teyvat Interactive Map for a comprehensive log of starconch locations.

Farm Fatui Agents for Recruit's Insignias. They're spread out all over Teyvat, so you have your choice of areas for farming. Usually they'll be in a group full of diverse elements (Hydro, Pyro, Electro, and Geo), so it's good to not rely on a single element farming party. (Though, you can do what you want! With enough DPS, single element parties are fine.)

Runic Fangs are dropped by the new weekly boss in The Chasm, the Ruin Serpent. It's not a particularly difficult boss, but can be tedious to farm. The Serpent dives in and out of the ground, and it doesn't take damage while underground. There's also a unique mechanism that requires use of the