Union Arena Slime Deck Guide: Green Milim Build 2026

Updated October 19, 2026: we rebuilt this guide around Bandai's recommended Green list. The old version built the deck around Milim TSK-1-084, which isn't in either Green list Bandai posted, and it got the Damage keyword wrong: Damage (3) means a hit deals 3 damage, it doesn't triple anything. TSK-1-084 also isn't free under its Demon Lord condition; it just comes in active.

The Union Arena Slime deck list

List: Bandai's Green "That Time I Got Reincarnated as a Slime" deck from the official Recommended Decks by Title page (revealed June 19, 2026, via Bandai TCG+); card text from the official UNION ARENA card list.

Every character in the list is a Demon Lord. "Energy" is what you need on your energy line before you can play the card.

What each part does

Two Raid Milims, two jobs. Milim TSK-1-085 needs eight energy. When played she sidelines one of the opponent's sites and gets Snipe, so she can pick a front-line character to attack and it can't be blocked. When she attacks you choose Impact (1) or Damage (3) for the turn. Damage (3) is the closer: a direct hit from her takes three life instead of one.

Milim TSK-1-085. Image: official UNION ARENA card list (Bandai).

Milim TSK-2-066 needs nine and is removal. She sidelines a character on the opponent's front line, and if you play her on your own turn she also sends a second one back to their hand. That bounce has a price: she drops to your sideline at the end of the opponent's next attack phase, leaving the Milim underneath. The ability works once per turn.

Milim TSK-P-006 is the sturdy one. It comes in active and can't be sidelined or hit by BP reduction until your next turn. Before a Slime Rare Battle, a player asked how that works against Diablo's sideline effect. u/Noxablaze explained: "If Milim isn't the only card on your Front Line, the opponent gets to pick who to sideline. You can choose Milim as the target if she was played the turn before".

Milim TSK-2-066 and TSK-P-006. Image: official UNION ARENA card list (Bandai).

The rest is ramp and digging. Frey, Milim TSK-P-003 and both Ramiris Raid lines make extra Green energy, which is how an eight-energy card gets played at all. Milim TSK-2-064 is the search: its look at three finds a Raid Milim about 41% of the time and some Milim more than four times in five, because 22 of the 50 cards are Milims.

How often the Raid comes together

Raid needs the SR plus a Milim already on your field. With 8 SRs and 14 lower Milims, the pair is in your opening seven about two times in three, and by your 10th card more than four times in five, before any searching. That's the deck's real strength: the finish shows up. The question is whether your energy has caught up by then.

Source: our simulation, 200,000 shuffles of Bandai's Green list. Ignores Milim TSK-2-064's search, so real numbers are higher.

The energy curve

The gap between five and eight is the whole game plan. Nothing in the middle wins on its own, so every early turn is about energy generation, not board.

Matchups and results

There's no matchup data to report. Union Arena has no public win-rate tracker, and the official top-placing page has no Slime deck in it as of October 19, 2026. When a player asked which Slime deck was best for Rare Battles, the most useful answer came from u/TeaVegetable7657: "They all seem to have potential. I’d wait for regional or big tournaments and see what places." (comment). That's still where it stands.

The best footage we found is a seeded game from a Summerfest tournament against Purple Reze:

What we'd change

Nothing in Bandai's list, and we'd leave out Milim TSK-1-084, the card the old version of this guide was built on. It needs six energy and 2 AP for a 4000 BP body with Damage (2), and its Demon Lord condition only makes it come in active. Milim TSK-P-006 costs less energy, comes in active without a condition and protects itself.

Milim TSK-1-084, the one we'd leave out. Image: official UNION ARENA card list (Bandai).

For the rules side, our Raid mechanic explainer covers how Raid stacks work, and the Union Arena current meta tier list shows which decks are actually placing. If you want a deck with results behind it, the SAKAMOTO DAYS deck guide is the place to start.

How we checked this: on October 19, 2026 we pulled Bandai's Green Slime list from the official Recommended Decks page through Bandai TCG+, read every card in it on the official UNION ARENA card list, checked the top-placing page for Slime results, and simulated 200,000 shuffles of the list with a short script.