Kathril, Aspect Warper costs {2}{W}{B}{G} and is a Legendary Nightmare Insect. When it enters, it puts a flying counter on any creature you control if a creature card in your graveyard has flying, and repeats this for first strike, double strike, deathtouch, hexproof, indestructible, lifelink, menace, reach, trample and vigilance. Then it gets a +1/+1 counter for each counter put on a creature this way. The more keywords in your graveyard, the more counters you get, so the deck wants a graveyard full of keyword creatures.
The precon already has the keyword creatures and the reanimation, including Zetalpa, Odric, Akroma, Grisly Salvage and Nyx Weaver. 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 Kathril decks, plus lift, which shows how much more often a card turns up in Kathril decks than in decks that could play it.
Looking for the unmodified list first? Read the Symbiotic Swarm precon guide.
What is holding the deck back
Not enough keyword creatures and graveyard fillers
Leyline Prowler, Nighthawk Scavenger, Shrike Force and Bassara Tower Archer carry several keywords for a few mana. Buried Alive, Jarad's Orders, Skull Prophet and Vile Entomber put them into the graveyard. They are among the top-scoring cards the precon leaves out.
Goad Auras and cards outside the lists
Martial Impetus, Parasitic Impetus and Predatory Impetus, Cartographer's Hawk, Angel of Finality, Reveillark, Soul of Innistrad, Soulflayer, Nikara, Yannik, Vitality Hunter and Bonder's Ornament are not cards Kathril decks usually play.
A top-heavy deck
The deck has 14 nonland cards at mana value six or more and 38 lands, so cheap creatures and cheap fillers matter.
The 12 swaps
Each pair shows the numbers for the card coming out and the card going in. Click a card image to zoom.
Bonder's Ornament is a three-mana rock that taps for any color. It is not a card Kathril decks usually play.
Leyline Prowler is a 2/3 Nightmare Beast for {1}{B}{G} with deathtouch and lifelink. It taps for one mana of any color. A three-drop that is a mana rock with two keywords, and the highest-scoring creature the precon leaves out.
Angel of Finality is a four-mana 3/4 flyer that exiles a graveyard, including yours. It is not a card Kathril decks usually play.
Shrike Force is a 1/3 Bird Knight for {2}{W} with flying, double strike and vigilance. A three-drop with three keywords, which is three counters for Kathril once it is in the graveyard.
Cartographer's Hawk is a two-mana 2/1 flyer that fetches a Plains. It is not a card Kathril decks usually play.
Nighthawk Scavenger is a Vampire Rogue for {1}{B}{B} with flying, deathtouch and lifelink. Its power is 1 plus the number of card types among cards in your opponents' graveyards. A three-drop with three keywords.
Nikara, Lair Scavenger is a three-mana 2/2 with menace and a partner that is not in the deck. It is not a card Kathril decks usually play.
Skull Prophet is a 3/1 Human Druid for {B}{G}. It taps for {B} or {G}, or taps to mill two cards. A two-drop that ramps and fills your graveyard.
Reveillark is a five-mana 4/3 flyer that returns two small creatures when it leaves the battlefield. It is not a card Kathril decks usually play.
Bassara Tower Archer is a 2/1 Human Archer for {G}{G} with reach and hexproof. A two-drop with two keywords that Kathril can count.
Soul of Innistrad is a six-mana 6/6 with deathtouch that returns creatures from the graveyard to your hand. It is not a card Kathril decks usually play.
Vile Entomber is a 2/2 Zombie Warlock for {2}{B}{B} with deathtouch. When it enters, you search your library for a card and put it into your graveyard. A four-drop that puts a keyword creature into the graveyard for Kathril.
Soulflayer is a six-mana 4/4 with delve that takes keywords from creatures exiled from your graveyard. It is not a card Kathril decks usually play.
Sunblade Angel is a 3/3 Angel for {5}{W} with flying, first strike, vigilance and lifelink. A six-drop with four keywords that Kathril counts once it is in the graveyard.
Vitality Hunter is a four-mana 3/4 lifelinker with monstrosity. It is not a card Kathril decks usually play.
Oketra the True is a 3/6 Legendary God for {3}{W} with double strike and indestructible. It can't attack or block unless you control at least three other creatures, and for {3}{W} it creates a 1/1 Warrior with vigilance. A four-drop with two keywords that makes tokens.
Yannik, Scavenging Sentinel is a four-mana 3/3 vigilance Hyena Beast that needs its partner. It is not a card Kathril decks usually play.
Glissa Sunslayer is a 3/3 Phyrexian Zombie Elf for {1}{B}{G} with first strike and deathtouch. Whenever it deals combat damage to a player you choose one: draw a card and lose 1 life, destroy target enchantment, or remove up to three counters from a permanent. A three-drop with two keywords that draws cards.
Martial Impetus is a three-mana Aura that goads the enchanted creature. It is not a card Kathril decks usually play.
Bleeding Effect costs {2}{W}{B}. At the beginning of combat on your turn, creatures you control gain flying until end of turn if a creature card in your graveyard has flying, and the same for first strike, double strike, deathtouch, hexproof, indestructible, lifelink, menace, reach, trample and vigilance. A four-mana enchantment that gives your team every keyword in your graveyard every turn.
Parasitic Impetus is a three-mana Aura that goads and drains. It is not a card Kathril decks usually play.
Jarad's Orders costs {2}{B}{G}. You search your library for up to two creature cards, reveal them, put one into your hand and the other into your graveyard. A four-mana sorcery that tutors a creature and fills the graveyard with a keyword creature.
Predatory Impetus is a five-mana Aura that gives +3/+3 and goads. It is not a card Kathril decks usually play.
Buried Alive costs {2}{B}. You search your library for up to three creature cards and put them into your graveyard. A three-mana sorcery that fills the graveyard with three keyword creatures, which Kathril counts when it enters.
The full swap list
Cut
- Bonder's Ornament
- Angel of Finality
- Cartographer's Hawk
- Nikara, Lair Scavenger
- Reveillark
- Soul of Innistrad
- Soulflayer
- Vitality Hunter
- Yannik, Scavenging Sentinel
- Martial Impetus
- Parasitic Impetus
- Predatory Impetus
Add
- Leyline Prowler
- Shrike Force
- Nighthawk Scavenger
- Skull Prophet
- Bassara Tower Archer
- Vile Entomber
- Sunblade Angel
- Oketra the True
- Glissa Sunslayer
- Bleeding Effect
- Jarad's Orders
- Buried Alive
What to keep
These cards are doing the deck's heavy lifting. Do not cut them.
- Zetalpa, Primal Dawn$0.21
Played in 93% of Kathril decks. Has flying, double strike, vigilance, trample and indestructible, which is five keywords for Kathril. - Grisly Salvage$0.14
Played in 69% of Kathril decks. Puts a creature or land into your hand and the rest of the top five into your graveyard. - Odric, Lunarch Marshal$0.49
Played in 68% of Kathril decks. Shares keywords among your creatures at the start of each combat. - Akroma, Angel of Wrath$2.18
Played in 67% of Kathril decks. Has flying, first strike, vigilance, trample and haste, which are five keywords for Kathril. - Nyx Weaver$0.24
Played in 61% of Kathril decks. Mills two cards each upkeep and can return a card from the graveyard.
If you want to spend more
These are strong but sit outside a budget upgrade. Prices are the cheapest paper printing.
- Scavenged Brawler$3.48
A six-mana Construct with flying, vigilance, trample and lifelink that can give four counters from the graveyard. It costs more than a budget upgrade should. - Eerie Ultimatum$2.28
A seven-mana sorcery that returns permanent cards with different names from your graveyard. It costs more than a budget upgrade should.
Symbiotic Swarm already has the keyword creatures, the reanimation and Kathril itself. The upgrade is cheap creatures with many keywords and ways to put them in the graveyard, in place of goad Auras and cards that Kathril decks leave out. These twelve swaps cost about $10 in total.
Want a full 100-card list built around Kathril, Aspect Warper from today's data?
Build with The Oracle →Frequently asked questions
What are the best upgrades for the Symbiotic Swarm precon?
Using data from 4,426 Kathril decks, the highest-scoring additions are Buried Alive (for Predatory Impetus), Leyline Prowler (for Bonder's Ornament) and Oketra the True (for Vitality Hunter). The full list has 12 swaps, each scored with synergy, inclusion and lift.
How much does it cost to upgrade Symbiotic Swarm?
All 12 swaps cost about $9.89 at the cheapest paper printings (TCGplayer market prices via Scryfall, 2026-10-28). If you want to spend more, the guide also covers Scavenged Brawler ($3.48) and Eerie Ultimatum ($2.28).
What should I cut from Symbiotic Swarm?
The weakest cards for this commander are Bonder's Ornament, Angel of Finality and Cartographer's Hawk. The guide explains the reason for every cut, and swaps each one for a card that scores higher.
Which cards should I keep in Symbiotic Swarm?
Keep Zetalpa, Primal Dawn, Grisly Salvage, Odric, Lunarch Marshal, Akroma, Angel of Wrath and Nyx Weaver. These are the cards doing the deck's heavy lifting.
What does Kathril do?
Kathril, Aspect Warper costs {2}{W}{B}{G} and is a Legendary Nightmare Insect. When it enters, it puts a flying counter on any creature you control if a creature card in your graveyard has flying, and repeats this for first strike, double strike, deathtouch, hexproof, indestructible, lifelink, menace, reach, trample and vigilance. Then it gets a +1/+1 counter for each counter put on a creature this way. The more keywords in your graveyard, the more counters you get, so the deck wants a graveyard full of keyword creatures.
More Commander 2020 (Ikoria) upgrade guides
How the numbers work
Inclusion is the share of Kathril, Aspect Warper decks (4,426 of them when this was written, 2026-10-28) 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 Kathril decks, which flatters every card the precon contains. Lift is high for many keyword cards because few decks play them outside a keyword 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.