Serpent's Eye Geas Robe (M) is crafted with Tailoring in Mabinogi (clothes). This page lists everything needed to make it, checked against the game as it exists today. The interactive planner lives in the Tailoring Companion.
How to get the sewing pattern
The sewing pattern is rank 1 and survives 30 uses; every crafting attempt spends one use.
Feth Fiada (10 Uses): Clear the Feth Fiada mission from the quest board in Tech Duinn.. Requires a total level of 3,000 or higher, party of up to 4.
Materials
Expect about 7 attempts per finished item (15% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
3× Scented Silk — Gathered in the Forest of Four Seasons fairy area.
5× Fine Leather Strap — weaving rank 6 on a spinning wheel
2× Geas Core — Drops from Feth Fiada, Revived Illusion, or Seven Nightmares Tech Duinn missions.
Finishing (once per item)
5× Finest Leather Strap — weaving rank 3-1 on a spinning wheel
2× Finest Finishing Thread — Buy directly from any general goods NPC shop.