Muffler Robe is crafted with Tailoring in Mabinogi (robe). 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 E and survives 30 uses; every crafting attempt spends one use.
Neid: Defeat Neid, the field boss that lives in Lake Neagh inside Abb Neagh.. Fought in the open field, no special pass needed, but it hits hard and works best with a group.
Materials
Expect about 3 attempts per finished item (40% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
1× Common Fabric — buy from NPC shops
1× Common Silk — buy from Seal Merchant (Mondays) for seals, or weave rank F
1× Thick Thread Ball — Hot-Air Ballooning reward (11-15 stars) or gift from Simon
Finishing (once per item)
1× Fine Finishing Thread — Buy directly from any general goods NPC shop.