Get Completionist Cape and Master Quest Cape first both are tracked as prerequisites on this cape's tab — Trimmed Completionist is built directly on top of them, not a separate grind from scratch.
The requirement list grows over time as new content releases, Jagex periodically adds new achievements to the trim list — this is the most "living" of the four capes.
84 trim-exclusive achievements these are on top of (not instead of) everything already required for Completionist Cape and Master Quest Cape, which are tracked on their own tabs.
Buying isn't a separate requirement once Completionist Cape, Master Quest Cape and everything above are met, purchase from the same Museum guard for 5,000,000 coins.
Iron accounts: budget the full time on E-I-E-I-O and E-I-E-DI-NO both breeding-log achievements list a faster route "if you buy perfect breeding pairs instead of breeding them yourself" — that shortcut needs player trading, which iron accounts don't have, so the full ~70-day and ~90-day estimates already listed for them are the realistic ones. Only daily breeding cycles advance either log regardless of play time, so start both on day one rather than late in your account's life.
Hardcore accounts: Reaper Crew is the requirement to plan around it wants a single kill of each of 55 bosses, and unlike the minigame content flagged on Completionist Cape's own tab, those are ordinary deaths — one of them ends hardcore status and drops you to a regular iron account. A boss instance set to practice mode is a safe death, so learning an unfamiliar fight there costs nothing but time; the kill that counts still has to happen on a real instance afterwards. This is the requirement to over-prepare for rather than the one to push through quickly.
Achievements (84)
Activities
Build Them All! — Build all of the Treasure Trail hidey-holes. You can find a complete list of hidey-holes at the noticeboard by Zaida. (~45 min)
Champions. What Champions? — Defeat all champions in the Champions' Challenge. (12-20 hrs)
Eastern Explorer — Explore the Eastern Lands as far as the Shield from your port. Distance travelled: (X/4,100,000) (4-7 hrs)
Get Tooled Up — Fill up your tool belt. (~1 hr)
Globetrotter — Purchase the full Globetrotter outfit. (7-12 hrs)
Jack of the Circus — Obtain all circus clothing from Balthazar Beauregard's Big Top Bonanza. (8 weeks)
Master Angler — Purchase the champion's tackle box from the Fish Flingers fisherman. (2-3 hrs)
Master Otto — Complete all barbarian training with Otto, at his grotto west of Baxtorian Falls. (1-2 hrs)
Nomad's Mirage — Defeat the memory of Nomad and loot one of his bounty chests. (~1 hr)
Out of this World — Unlock everything in the Shooting Star Reward Shop. (X/3) (~27 hrs)
Penguin Adoption Agency — Adopt Sheldon the penguin by tracking penguin spies around the world. (6 weeks)
Raptor's Revenge — Complete the Ungael combat activity on hard mode. (~15 min)
Scrolling in the Deep — Find every scroll piece in Player Owned Ports. (~10 min)
Combat
A Song of Ice and Ire II — Defeat the Arch-Glacor at 100% enrage. (X/100) (~15 min)
Conquered Everyone's Heart — Reach maximum reputation with all Heart of Gielinor factions. (133 days)
Death Effect — Unlock all permanent effects from Death's Store. (X/8) (~24 hrs)
Finish Him! — Personally defeat Vorago with the Maul of Omens. (1-2 hrs)
Jail break — Free each of the baby dinosaurs from the jail cells within the Rex Matriarch lair. (2-3 hrs)
My Goebie Homies — Obtain maximum reputation with the goebies on Mazcab. (~1 hr)
Reaper Crew — Defeat listed bosses at least once. (X/55) (~10 min)
Shadows Below — Survive the shadow beneath the barrows. (7-12 hrs)
Telos If You're Angry II — Defeat Telos at 100% enrage. (X/100) (~15 min)
War. What Is It Good For? — Buy all unlocks and upgrades from War's store. (X/2) (~10 min)
Exploration
All Your Energies — Unlock the energy-gathering scrimshaw scroll from Waiko ports reward shop. (~30 min)
Bone to Pick With You — Unlock the bonecrusher upgrade from Waiko reward shop. (~30 min)
Canoe Fix It? Yes You Can! — Repair all the canoe stations around Havenhythe. (X/4) (~10 min)
Don't Crush My Memories — Unlock the memory-crushing scrimshaw scroll from the Waiko ports reward shop. (~30 min)
Elder Wisdom — Earn the Wisdom of Anima fletching perk for all the Elder God arrow types. (~1 hr)
God of the Grind — Fully repair the statue of Het. (1-2 hrs)
Jurassic Perk — Discover all the totem pieces on Anachronia. (X/7) (2-3 hrs)
Master Builder — Fully upgrade the base camp on Anachronia. (65 days)
Mitts and Waders - Death Lotus — Unlock the death lotus gloves and boots scrolls from the Waiko reward shop. (~45 min)
Mitts and Waders - Seasinger — Unlock the seasinger gloves and boots scrolls from the Waiko reward shop. (~45 min)
Mitts and Waders - Tetsu — Unlock the tetsu gloves and boots scrolls from the Waiko reward shop. (~45 min)
Remotely Possible — Build the Remote Totem Access Point in the base camp on Anachronia. (~15 min)
Reputation - Class Crown — Earn tier 10 reputation with the imperial faction in Menaphos. (4-7 hrs)
Reputation - Lock, Stock and Barrel — Earn tier 10 reputation with the merchant faction in Menaphos. (4-7 hrs)
Reputation - Seagullible — Earn tier 10 reputation with the ports faction in Menaphos. (4-7 hrs)
Reputation - To the Bone — Earn tier 10 reputation with the worker faction in Menaphos. (4-7 hrs)
Salty — Fully explore what the Arc has to offer, and earn the right to claim the 'Salty' title. (2-3 hrs)
Sandy — Complete various achievements within Menaphos... and then some more to earn the right to claim the 'Sandy' title. (~10 min)
Sort of Crystally — Obtain the 'Dark Lord' title by unlocking a selection of titles from Prifddinas. (1-2 hrs)
The Golden Crocodile Hunter — Unlock all Hunter upgrades from Dundee's Shop. (1-2 hrs)
Um Pop — Meet all of the listed inhabitants of Um. (~1 hr)
Who Will Be Her Lover? — Complete the replica statue of Rhiannon in the Max Guild garden. (12-20 hrs)