Background
Preservation & Ruin created the planet Scadrial together from scratch after the Shattering.
Trell is a shard/or shard-like entity that is unknown to Harmony
Trellium is the metal of a known shard: https://wob.coppermind.net/events/69-shadows-of-self-release-party/#e6261
Possible shard candidates (at time of WoB): Devotion, Dominion, Preservation, Ruin, Odium, Honor, Cultivation, Endowment, or Autonomy
But not necessarily a shard: https://wob.coppermind.net/events/377-idaho-falls-signing/#e12232
Devotion and Dominion have spren-like cognitive splinters – seons and skai respectively
Seons are ‘devoted’ servants to their masters
Skai are described as ‘evil seons’ (https://wob.coppermind.net/events/247-ancient-17s-qa/#e5540)
Avatars of Shards can be imbued with an intent and can operate after a shard’s vessel has died
The Mist continued to snap people on Scadrial after Ati died
Theory
Preservation & Ruin pooled their Investiture and used a Dawnshard to create the planet Scadrial
Ruin agreed to this use of Investiture on condition that he could destroy the planet eventually
The Dawnshard that allowed for the planet’s creation is still on Scadrial and is currently being protected by Harmony
A primary of Intent of Dominion shard is ‘to dominate’
The skai are evil counterparts to seons who are described as being helpful and obedient. The opposite of this could be 'dominating'.
Trell is an avatar of Dominion
Etymologically the word Trell is related to a Norse word meaning ‘slave or thrall’. This aspect fits as an aspect of Dominion that has an Intent to dominate
Trellium is Dominion’s metal
Trellium as a hemolurgic spike allowed for control over Paalm and the hemalurgic chimeras created by her. This fits with an Intent of domination.
Harmony is unaware of what Trellium is and that it comes from Dominion because the Vessel of Dominion is dead.
His knowledge of Shards and wider Realmatic Theory comes from self-study and from whatever the other Shard Vessels and people like Hoid tell him
Trell's ultimate purpose is to get the Dawnshard on Scardrial
Open Questions
As an avatar of Dominion, Trell was able to move a large amount of Dominon’s Investiture off planet. Could this be connected to Kelsier (and by extension the Ghostbloods) goal to learn how to move large amounts of Investiture off planet?
Could Odium’s decision to destroy Dominion (and Devotion) be influenced by what Dominion’s plans were?
What (if any) is the connection to the man named Trell on Taldain?