Combo · ENGINE

814.1.d.1 ties Shield to the Defender designation, which is why Fortified Position's 'this combat' is the pool's exactly-right duration on a 2-Energy Tank

4 cards · calm · verified

Pieces

• Mutated Mouser ×3 UNL-036 · payoff · calm

  [Shield 2] (+2 Might while I'm a defender.) [Tank] (I must be assigned combat damage first.)

• Fortified Position ×1 OGN-279 · battlefield

  When you defend here, choose a unit. It gains [Shield 2] this combat. (+2 Might while it's a defender.)

Payoff

Deck

• Mutated Mouser is mono-Calm and Fortified Position is colourless, so 103.1.b.1 is satisfied by any legend carrying Calm - the census gives sixteen names, among them Nine-Tailed Fox (OGN-255), Blind Monk (OGN-257), Unforgiven (OGN-259), Radiant Dawn (OGN-261) and Fire Below the Mountain (SFD-189).
• Neither card is Signature (checked against data/cards.json) and neither appears in data/legality.json in either format.
• The battlefield has to come up: 485.4.a has each player provide three and only one of yours is used, 485.5 and 487.5 say it is selected RANDOMLY, and 103.4.c plus Tournament Rules 402.1 forbid three copies of the same battlefield name - so this line is a draw, not a certainty.

Run play

• Fortified Position holds the battlefield, and one Flurry before the attack takes it

Prerequisites

• 814.1.d AND 814.1.d.1 WERE UNCITED AND THEY ARE WHY THE DURATION FITS. 814.1.d: 'Being a defender means the Unit has gained the Defender designation during Combat.' 814.1.d.1: 'Shield remains in effect as long as the Unit maintains the Defender designation.' Fortified Position grants '[Shield 2] this combat' - the only SHIELD grant in the pool tied to a combat rather than a turn (measured 2026-09-09: the phrase 'this combat' appears on exactly two cards, OGN-279 and SFD-110 Fiora Peerless, whose clause doubles Might and grants no keyword; every other Shield grant reads 'this turn' or is a permanent static) - and 814.1.d.1 makes those two windows the same window. Nothing is wasted at either end.
• THE SUM, AND WHY A PRINTED SHIELD COUNTS TOWARD IT. 814.1.b: 'Shield is formatted as "Shield [X]".' 814.1.b.2: 'The X is referred to as the Shield Value.' 814.1.b.3: 'If X is omitted, it is presumed to be 1.' 814.2 then sums, and its worked example settles that a PRINTED Shield joins the sum: 'Stalwart Poro has Shield. It is chosen as the target of Block, which says "Give a unit [Shield 3] and [Tank] this turn." After Block resolves, Stalwart Poro has Shield 4 this turn.' So the Mouser's printed 2 plus the battlefield's granted 2 is Shield 4 and a Might-1 body defends as a 5.
• WHAT THAT COSTS THE ATTACKER, IN THE RULES' OWN ARITHMETIC. 142.4.b: 'Lethal Damage for a Unit is a non-zero amount greater than or equal to that Unit's Might', and 465.2.c reads current Might at assignment, so five damage has to be spent on a two-Energy body. 815.1.b makes that spending compulsory and first - it is short for 'I must be assigned lethal damage before any other unit with the same controller as me that does not have [Tank] during the Combat Damage step' - and 815.1.c.2 makes every other body of yours an INVALID assignment until it has been. A garrison of three Mousers is fifteen damage of toll before anything else of yours can legally be assigned any.
• THE KEYWORD IS INVISIBLE OUTSIDE THE COMBAT, WHICH CUTS BOTH WAYS. 814.1.c is 'While I am a defender, I have +X [M]', so the Mouser reads Might 1 for every Main-Phase count - a Mighty threshold, a 'Might 3 or less' removal gate, an excess-damage sum on offence. It is a 5 exactly when it is being killed and a 1 the rest of the time.
• AND IT IS A DEFENDER-ONLY ANSWER. 814.1.d requires the Defender designation, which 464.2.c.3 hands out inside a Combat, so none of this applies when you attack; this is a wall, and the pool's own contrast is [Assault] (807.1.c), which is the mirror image on offence. 814.3 closes the keyword - 'Shield, and whether or not a unit has Shield, is a characteristic of the Unit and may be checked or referenced by other Game Effects' - and 815.2 makes a second [Tank] grant on the Mouser redundant.
• THE GRANT IS ONCE PER COMBAT AND IT CHOOSES. 'When you defend here, choose a unit' - one body per combat, and 809.1.c would tax a [Deflect] target but this chooses your OWN unit, so nothing is paid. Three Mousers means the other two are at Shield 2 while the chosen one is at 4; the toll is 3 + 3 + 5 = 11, not 15, unless a second grant arrives.
• A COUNTER IN THE ENGINE'S OWN DOMAIN ANSWERS BOTH CHEAP BREAKS - ADDED 2026-10-14 (#353, from the run play docs/plays/2026-10-14-fortified-position-holds-and-one-flurry-before-the-attack-takes-it.md). OGN-045 Defy is Calm, E1 + 1 Power: '[Reaction] (Play any time, even before spells and abilities resolve.) Counter a spell that costs no more than :rb_energy_4: and no more than :rb_rune_rainbow:.' Flurry of Blades costs E1 and UNL-107 Stare Down costs E2, so Defy counters either. Stare Down is the other cheap break, Body, E2: 'Choose a friendly unit and a battlefield. Move all enemy units at that battlefield with less Might than the chosen unit to their base. Gain 1 XP.' Out of combat every Mouser is a 1, so any of their bodies with Might 2 or more sends every Mouser home and empties Fortified Position without killing one. It carries no keyword, so 155 confines it to their Main Phase, which is where Defy has to be held up. Of the Calm counters, Defy is the cheapest whose condition both breaks always meet. VEN-039 Crumbling Sands costs the same, E1 + 1 Power, but counters only 'if an opponent has played another spell this turn', which a lone Flurry does not meet. OGN-064 Wind Wall (E3 + 2 Power) and UNL-044 Flurry of Feathers (E4 + 2 Power, through its 'Counter a spell' mode) carry no condition and cost more. SFD-045 Not So Fast does not answer the Flurry: it counters only a spell or ability 'that chooses a friendly unit or gear', and the Flurry chooses nothing (355.10.d).
• THE ATTACKER'S TRIGGER GOES ON THE CHAIN FIRST, SO THE GRANT IS AIMED KNOWING WHERE IT LANDED - ADDED 2026-10-14 (#353, from the same run play). 464.2.e.1: 'The Attacking player, who has Focus, places Triggered Abilities on the Chain first, followed by all non-Defender players in Turn Order, followed by the Defending Player.' 337.1 finalizes the oldest pending item first, and an ability's choices are made while it is finalized (399, 355), so an attack trigger such as OGN-130 Crackshot Corsair's ('When I attack, deal 1 to an enemy unit here.') has its target before you choose the grant's. In the play's combat (Corsair 3 + Diplomat 2 against two Mousers, the Corsair's 1 on the first) the grant on either Mouser costs exactly one: killing both takes 2 + 5 or 4 + 3, and their 5 reach neither total, so exactly one Mouser dies. Without the grant both Mousers are 3s, their 5 are 2 + 3 and kill both, your 6 still kill both attackers, and 466.5.b leaves Fortified Position uncontrolled. The grant's +2 is the margin between keeping the battlefield and an empty one.
• ONE ENERGY AT REACTION SPEED ANSWERS THE BODY THIS ENGINE STANDS ON (Mutated Mouser (M1 x3)). OGN-133 Flurry of Blades is Body, 1 Energy: "[Reaction] (Play any time, even before spells and abilities resolve.) Deal 1 to all units at battlefields." 143.2.a kills a unit whose marked damage equals or exceeds its Might and 142.4.b defines Lethal Damage as "a non-zero amount greater than or equal to that Unit's Might", so one damage is lethal to every body of Might 1 or less. RUNNING MORE COPIES IS NOT A DEFENCE: 370.1.a.2 makes events simultaneous when they "are all the result of the same Game Action", so the sweep kills every copy at once. And because it carries [Reaction], 813.1.c.1 lets it be played "during Closed States on any player's turn" - it never has to be cast a turn early the way the base-reaching removals do, and it can land in response to the very trigger this engine exists to fire. CORRECTED 2026-10-14 (#353, from the run play docs/plays/2026-10-14-fortified-position-holds-and-one-flurry-before-the-attack-takes-it.md): that last claim is wrong for this engine. Its trigger is Fortified Position's defend trigger, and 383.4.f.2 puts it on the chain only after the designation: 'These Triggered Abilities are put on the Chain as Pending Items after the Unit these effects correspond to gains the Defender designation during Combat.' By then every Mouser is a defender and a 3 (814.1.c, the printed Shield 2 on Might 1), so 1 damage is not lethal. Cast in response to the grant, the Flurry kills no Mouser by itself. In the play's combat (OGN-130 Crackshot Corsair 3 + UNL-092 Demacian Diplomat 2 against two Mousers) the extra 1 on every body still turns the fight into a mutual wipe, and 466.5.b leaves the battlefield uncontrolled. The window where it kills is OUTSIDE the combat, where every Mouser is a 1: the opponent's Main Phase before the attack (155), or a Closed State on your turn (813.1.c.1). Cast there, one Energy kills every Mouser at Fortified Position at once, and 323.6 takes the battlefield at the next cleanup in an Open State. WHAT PROTECTS IT: this entry's cards are calm, so the second domain is still free and CHOOSING IT DECIDES WHICH PROTECTION YOU GET - 103.1.b allows exactly one partner, so these are alternatives and not a list you can run together. only if the second domain is FURY: VEN-018 Rage Amplifier (gear, 'Your units have +1 Might' - the only UNCONDITIONAL board-wide one, +2 while Empowered) | only if the second domain is ORDER: OGN-243 Darius, Executioner ('Other friendly units have +1 Might HERE' - his battlefield only, and never himself); OGS-013 Garen, Commander (same clause as Darius, same limits) - CORRECTED 2026-10-14 (#353, from the same run play): both cost E6 + 1 Power, which is six runes, one exhausted for the Energy and then recycled for the Power (164.2.a, 164.2.b). Going first that is your T3 at the earliest, played straight to Fortified Position (355.2.a, 'By default, Valid locations include the controller’s Base or a Battlefield the controller controls.'). It covers their T3 and not their T2, when the first Mouser already stands there alone; a three-copy Flurry is in their hand by their T2 (six of 39 cards seen) in 40.30% of games, the play's figure, re-derived here as 1 - C(36,6)/C(39,6). Going second it is later still, which the play does not walk: your T2 has five runes (430.4.a plus 485.7's extra one), so the first turn of theirs it can cover is their T4 | only if the second domain is MIND: UNL-077 Soul Shepherd ('Your TOKEN units have +1 Might' - tokens only, nothing for a printed body); SFD-089 Rumble, Scrapper ('Your MECHS have +1 Might' - Mech tag only). A single-target pump is no use against a sweep that hits every body at once, which is why only permanent, board-wide sources are listed.

Steps

1. Bring Fortified Position as one of your three battlefields and establish Control of it (190.1, 466.5) - its text is live only for its Controller (190.6.d).
2. Stand one or more Mutated Mousers there. Each is 2 Energy for a 1-Might body with printed [Shield 2] and [Tank].
3. When the opponent attacks, 464.2.c.3 designates your bodies Defenders and 814.1.d starts the Shield.
4. The battlefield's trigger fires - 'When you defend here, choose a unit. It gains [Shield 2] this combat' - and 814.2 sums it with the printed value: the chosen Mouser is Shield 4.
5. 465.2.c reads current Might, so that Mouser is a 5. 815.1.b and 815.1.c.2 force the attacker to assign five to it before any non-Tank body of yours is a legal assignment at all.
6. 814.1.d.1 keeps the Shield up for as long as the designation lasts, i.e. the whole combat, and 466.1.a.1's Combat Cleanup then heals the damage.

Per iteration

one combat in which the attacker spends 5 damage on a 1-Might body before any other unit of yours may legally be assigned damage

How it ends

engine - a 2-Energy body that costs five damage to remove and must be removed first, for as long as the combat lasts; nothing here scores

Sources

Published elsewhere

• Riftbound Core Rules, Last Updated 2026-07-16 (data/Riftbound-Core-Rules-2026-07-16.txt) 2026-07-16

Walked here, in this project

• Hand walk 2026-09-09, issue #191 - uncited Core Rules sub-rules 500-899 2026-09-09 record

Walked against Core Rules 2026-07-16

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