Trial missions are a retired, specially designed sets of missions, along with specifically modified tilesets and functions, often with unique mechanics and obstacles not found in any other mission type. Trial missions are significantly more difficult and complex than the rest of the mission types, featuring significantly higher enemy levels and special mission modifiers. To this end, players can form a tandem squad of eight players to even the odds of completion. Should they wish for additional challenge, players can also form a squad with fewer members, four players minimum. Trial missions will automatically fail if there are fewer than four players present in the squad.
Two Trials were released during the gamemode's lifetime:
- The Law of Retribution, where the Tenno were tasked hunting down, cornering and bringing Councilor Vay Hek to justice for the crimes he committed during Operation: Eyes of Blight.
- The Jordas Verdict, where the Tenno followed up on the lead Cephalon Jordas gave them at the end of the The Jordas Precept, discovering a massive Corpus ship overrun with the Infested, harboring a monstrosity that could threaten the entire Origin System if left to fester and multiply.
Access[]
Each trial mission had an associated key that must be possessed by the hosting player in order to access trial recruitment. Keys were built from reusable blueprints which were available in the Market for 
100,000. The host's key was then consumed upon mission entry. As of Update 22.14 (2018-03-01) these blueprints are no longer available and any remaining in a players inventory have been refunded.
Nightmare Trials[]
Nightmare Modes of Trial missions are also available as more Trials are released. Nightmare Trials not only feature harder obstacles; they also add various modifiers, mechanics, and dangers that will require the players to push their coordination to their absolute best. Oftentimes, completing a Nightmare Trial features a "true" ending to the initial mission and may have different outcomes.
Nightmare trials require associated key blueprints and keys separate from their non-nightmare versions.
Rewards[]
Completion of Trial missions will award players the most exotic prizes in the solar system: a large sum of credits, an Arcane Enhancement, and their own respective emblems to mark their completion. Players can only claim these prizes once per day, though different trials (including Nightmare Modes) have separate timers. It is important to note that a player will still receive the reward if their timer refreshes during the trial.
When the Trial missions were retired indefinitely, all players who had completed at least one were rewarded with the Invati Sekhara badge in recognition for their achievement.