Morska, Undersea Sleuth costs {G}{W}{U} and is a 2/3. You have no maximum hand size, at the beginning of your upkeep you investigate, and whenever you draw your second card each turn you put two +1/+1 counters on Morska. Every Clue you crack is a second draw.
The precon already has the Clue makers and the doublers, including Academy Manufactor, Tireless Tracker, Erdwal Illuminator and Adrix and Nev, Twincasters. Each swap below pairs a cut with an add, and every card is scored with the same numbers the Oracle uses to build decks: synergy and inclusion from the Morska decks, plus lift, which shows how much more often a card turns up in Morska decks than in decks that could play it.
Looking for the unmodified list first? Read the Deep Clue Sea precon guide.
What is holding the deck back
Not enough cheap Clue makers
Alquist Proft, Lavinia, Deduce and Officious Interrogation make Clues for one to three mana, and Tamiyo's Journal and Forensic Gadgeteer make them every turn. They are among the top-scoring cards the precon leaves out.
Few payoffs for a second draw
Homunculus Horde copies itself and Private Eye makes Detectives unblockable whenever you draw your second card each turn, and Morska does it every time.
Expensive cards that do nothing for Clues
Hornet Queen is not a card Morska, and Organic Extinction, Aerial Extortionist and Hydroid Krasis are each played in about one Morska deck in four or fewer decks usually play.
The 13 swaps
Each pair shows the numbers for the card coming out and the card going in. Click a card image to zoom.
Hornet Queen is a seven-mana flier that makes four deathtouch Insects. It is not a card Morska decks usually play.
Tamiyo's Journal costs {5}. At the beginning of your upkeep you investigate, and for a tap and three Clues you search your library for a card. A second upkeep Clue, and a tutor at the end of the chain. It is the highest-scoring card the precon leaves out.
Ransom Note is a one-mana Clue that surveils and can goad or cloak. It is played in about one Morska deck in twelve.
Deduce costs {1}{U} at instant speed: you draw a card and investigate. It draws the second card of your turn and leaves a Clue behind.
Serene Sleuth is a 2/2 Detective for {1}{W} whose second ability needs goaded creatures. It is played in about one Morska deck in ten.
Alquist Proft, Master Sleuth is a 3/3 vigilance Detective for {1}{W}{U}. When it enters you investigate, and for {X}{W}{U}{U}, a tap and a Clue you draw X cards and gain X life. A Clue maker that draws many cards at once.
Sophia, Dogged Detective is a 3/4 for {1}{G}{W}{U} that makes a Dog and sacrifices artifact tokens for counters. It is played in about one Morska deck in eight.
Private Eye is a 3/3 Homunculus Detective for {1}{W}{U}. Other Detectives you control get +1/+1, and whenever you draw your second card each turn a Detective cannot be blocked. Morska is a Detective, so she hits every turn.
Magnifying Glass is a three-mana rock that investigates for {4}. It is played in about one Morska deck in seven.
Five Hundred Year Diary is a legendary artifact Clue for {3}{U} that enters tapped and taps for {U} for each Clue you control. A Clue that pays for the Clues, and it draws a card when you sacrifice it.
Aerial Extortionist is a 4/3 flier for {3}{W}{W} that exiles a permanent and lets its owner recast it. It is played in about one Morska deck in six.
Forensic Gadgeteer is a 2/3 Detective for {2}{U}. Whenever you cast an artifact spell you investigate, and activated abilities of artifacts you control cost {1} less, down to one mana. Cracking a Clue costs {1}.
Hydroid Krasis is an X creature that draws half X cards and gains half X life. It is played in about one Morska deck in five.
Kellan, Inquisitive Prodigy is a 3/4 flying, vigilance Detective for {2}{G}{U}. Whenever it attacks you destroy up to one target artifact, and draw a card if you controlled it, so you can destroy your own Clue for a card. Its adventure, Tail the Suspect, investigates for {G}{U} and lets you play an additional land.
Killer Service is a three-mana enchantment that makes Food and lets you sacrifice tokens for 4/4 Rhinos. It is played in about one Morska deck in six.
Lavinia, Foil to Conspiracy is a 2/3 vigilance Detective for {1}{W/U}{W/U}. Whenever you cast your second spell each turn you investigate, and it taps for {C}{C} during an opponent's turn. A Clue for the second spell, and mana at instant speed to crack it.
Selvala, Explorer Returned is a 2/4 that gives every player a card when it parleys. It is played in about one Morska deck in four, and the card goes to opponents too.
Homunculus Horde is a 2/2 for {3}{U}. Whenever you draw your second card each turn, you create a token copy of it, and every copy does the same. A token every turn that Morska draws two cards.
Organic Extinction is a ten-mana sorcery that destroys all nonartifact creatures, with improvise. It is played in about one Morska deck in four.
Officious Interrogation costs {W}{U} at instant speed. You investigate once for each creature controlled by the target players, and it costs {W}{U} more for each target beyond the first. Target yourself and you get a Clue for every creature you control.
Nadir Kraken is a 2/3 for {1}{U}{U} that grows and makes Tentacles whenever you draw, for {1} each time. It is played in about one Morska deck in five.
Jaheira, Friend of the Forest is a 2/3 Human Elf Druid for {2}{G}. Tokens you control have "{T}: Add {G}." Every Clue and Food is mana, and she is one of the top-scoring cards the precon leaves out.
Follow the Bodies is a three-mana sorcery with gravestorm that investigates. It is played in about one Morska deck in four.
Cyberdrive Awakener is a 4/4 flying artifact creature for {5}{U}. Other artifact creatures you control have flying, and when it enters each noncreature artifact you control becomes a 4/4 artifact creature until end of turn. Every Clue becomes a 4/4 flier for a turn.
Confirm Suspicions is a five-mana counterspell that investigates three times. It is played in about one Morska deck in four.
Piper Wright, Publick Reporter is a 1/2 Human Detective for {1}{U}. Whenever she deals combat damage to a player you investigate that many times, and whenever you sacrifice a Clue you put a +1/+1 counter on a creature. A two-drop Detective that turns Clues into counters.
The full swap list
Cut
- Hornet Queen
- Ransom Note
- Serene Sleuth
- Sophia, Dogged Detective
- Magnifying Glass
- Aerial Extortionist
- Hydroid Krasis
- Killer Service
- Selvala, Explorer Returned
- Organic Extinction
- Nadir Kraken
- Follow the Bodies
- Confirm Suspicions
Add
- Tamiyo's Journal
- Deduce
- Alquist Proft, Master Sleuth
- Private Eye
- Five Hundred Year Diary
- Forensic Gadgeteer
- Kellan, Inquisitive Prodigy
- Lavinia, Foil to Conspiracy
- Homunculus Horde
- Officious Interrogation
- Jaheira, Friend of the Forest
- Cyberdrive Awakener
- Piper Wright, Publick Reporter
What to keep
These cards are doing the deck's heavy lifting. Do not cut them.
- Academy Manufactor$8.01
Played in 81% of Morska decks. Every Clue is also a Food and a Treasure. - Tireless Tracker$0.23
Investigates on landfall and grows when you sacrifice a Clue. - Erdwal Illuminator$0.14
A 1/3 flier that investigates an additional time the first time you investigate each turn. - Detective of the Month$0.39
Makes a 2/2 Detective whenever you draw your second card each turn, and makes Detectives unblockable with the city's blessing. - Adrix and Nev, Twincasters$7.98
Doubles every token you create, including Clues.
If you want to spend more
These are strong but sit outside a budget upgrade. Prices are the cheapest paper printing.
- Bard, King of Dale$3.84
Doubles every extra draw and every token you create. It costs more than a budget upgrade should. - Proft's Eidetic Memory$2.13
Draws a card and puts counters on a creature when you draw more than one card in a turn. - Thorough Investigation$2.43
Investigates whenever you attack, and ventures into the dungeon when you sacrifice a Clue.
Deep Clue Sea already has the Clue makers and the doublers. The upgrade is cheap Clue makers and payoffs for the second draw, in place of expensive cards that do nothing for Clues. These thirteen swaps cost about $18 in total.
Want a full 100-card list built around Morska, Undersea Sleuth from today's data?
Build with The Oracle →Frequently asked questions
What are the best upgrades for the Deep Clue Sea precon?
Using data from 8,035 Morska decks, the highest-scoring additions are Tamiyo's Journal (for Hornet Queen), Forensic Gadgeteer (for Aerial Extortionist) and Officious Interrogation (for Organic Extinction). The full list has 13 swaps, each scored with synergy, inclusion and lift.
How much does it cost to upgrade Deep Clue Sea?
All 13 swaps cost about $18.39 at the cheapest paper printings (TCGplayer market prices via Scryfall, 2026-10-27). If you want to spend more, the guide also covers Bard, King of Dale ($3.84), Proft's Eidetic Memory ($2.13) and Thorough Investigation ($2.43).
What should I cut from Deep Clue Sea?
The weakest cards for this commander are Hornet Queen, Ransom Note and Serene Sleuth. The guide explains the reason for every cut, and swaps each one for a card that scores higher.
Which cards should I keep in Deep Clue Sea?
Keep Academy Manufactor, Tireless Tracker, Erdwal Illuminator, Detective of the Month and Adrix and Nev, Twincasters. These are the cards doing the deck's heavy lifting.
What does Morska do?
Morska, Undersea Sleuth costs {G}{W}{U} and is a 2/3. You have no maximum hand size, at the beginning of your upkeep you investigate, and whenever you draw your second card each turn you put two +1/+1 counters on Morska. Every Clue you crack is a second draw.
More Murders at Karlov Manor Commander upgrade guides
How the numbers work
Inclusion is the share of Morska, Undersea Sleuth decks (8,035 of them when this was written, 2026-10-27) that play the card. Synergy is how much more often they play it than other decks in the same colours. Oracle score is synergy × 0.6 plus inclusion × 0.4, the same blend The Oracle uses to rank cards for a deck. Lift compares how often the card appears in these decks with how often it could, capped at 8× here; it is shown for context and does not change the score.
Two cautions. Players who run the precon unmodified count as Morska decks, which flatters every card the precon contains. Lift is high for many Clue cards because few decks play them outside a Clue deck, so use lift to compare cards, not to judge one in isolation. A card the commander's decks do not usually play counts as 0 in the average score. Prices are the cheapest non-foil paper printing on TCGplayer (via Scryfall), in USD, and move daily.