From Destinypedia, the Destiny wiki
Missive(Growth) is an Exotic Quest that was released during the Season of Arrivals. It is the Exotic Quest for the Ruinous Effigy. It is acquired from the Prismatic Recaster. It requires the Season Pass to complete.
Complete the Interference Mission. This mission is the same as usual but ends in Zavala arriving to talk about a gift from the Tree of Silver Wings. Note: This requires completion of the 'Means to an End' quest.
Step 2: Gift
Collect 25 pieces of calcified light across Mars, Io, Titan, and Mercury. There are 10 pieces on Io, and 5 on Mars, Titan, and Mercury. If you open Nav Mode on your Ghost, there will be white markers with distance markers on them. These will lead you to the Calcified Light fragments.  Kill 15 of Savathun's Marionettes. They will appear as a variation of either Overload Taken Hobgoblines or Unstoppable Taken Phalanxes. They spawn on Titan and Io. They spawn in mini-events and in Contact events.
Step 3: Feed
In this step, you have to kill enemies with void damage, get precision multikills, and complete Gambit or Reckoning. Higher tiers of Reckoning, kills as an Invader, or Invader kills grant additional progress.
Once all the steps are complete, you will get an Exotic Engram that you will have to decode at the Umbral Decoder. Once this is done, you will have finished the Quest and the Ruinous Effigy will be yours!
- ^ [Forbes- Here Are The Quest Steps To Get Destiny 2's Ruinous Effigy Exotic And Its Catalyst]