TL;DR
Build the Defect Frost wall exactly like before, then bolt a real damage win condition onto it. Major Update 2 added a new Act 3 boss, Aeonglass, that punishes slow clears by feeding unplayable Wither cards into your hand. A pure block-and-stall list now loses to it. Stack Frost orbs and Focus for survival, lead your offense with the Lightning line (Tesla Coil now triggers twice), and treat the reworked Shatter as a double-evoke block burst rather than a damage finisher. Defragment early, fill the queue fast, and close the fight before Wither buries you.
What Changed in Major Update 2
The Frost Tank used to win by sitting still. You set up the orb engine, generated more block than any boss could spend, and waited out the fight. That plan is dead at the top of the run.
Major Update 2 (v0.107.1) replaced the old Act 3 boss with Aeonglass, a fight built specifically to beat the wall. Aeonglass runs a passive called Withering Presence: for every six cards you play, it slips an unplayable Wither card into your hand. A Wither does nothing on its own, but if it sits in your hand at end of turn it deals 3 damage to you (6 on higher Ascensions). On top of that, the boss periodically shuffles upgraded Withers into your deck, gains Strength, and hits hard every turn while it does. The longer the fight runs, the faster that self-damage climbs. Stalling for six turns is now the way you die.
The fix is simple to state: the Frost engine buys you time, and you spend that time landing damage. The block keeps you alive long enough to close. The damage is what actually closes.
The Build in Two Phases
Phase one is the orb engine: channel Frost, add orb slots, and find your first Focus. Phase two is stacking Focus until your block ceiling outruns incoming damage. The same cards carry both phases, so the transition is smooth. The one change from the old playbook is that you now commit a slot of your draft to a scaling damage outlet from Act 1, not as an afterthought.
Orb and Focus Primer
Every item:defect run lives inside the orb queue. At the start of each turn, every orb fires its passive. When the queue fills, the leftmost orb evokes automatically and leaves.
Frost orbs grant block on passive. At zero Focus, each Frost orb gives 2 block per turn. Focus is the scaling stat: every point adds +1 to the passive and evoke values of every orb except Plasma. Two Focus turns each Frost orb into 4 block per turn. Five Frost orbs at two Focus is 20 block every turn before you play a card.
Focus compounds, and that is the whole engine. One Defragment pays off across every orb, every turn, for the rest of the combat. The target state is five or six total Focus behind three or more Frost orbs in a five-slot queue. At that point your passive block alone soaks most of what Act 3 throws at you, which is exactly the runway you need to spend on offense.
Core Cards
Cold Snap is the most important common in the Defect pool. One energy deals damage and channels a Frost orb, so it builds the engine and defends at the same time. Take every copy until you have three, and consider a fourth in a long Act 1.
Glacier is the mid-game accelerant. It channels two Frost orbs in a single play, so one energy-rich turn can push three or four Frost sources into the queue at once. It is the highest-priority Act 2 pickup for this list.
Defragment is the Focus engine, and it matters more than ever. One energy, permanent Focus. Play it as early as possible every combat. You need the block ceiling up fast before Wither pressure mounts, and two early Defragments set that pace. Take it over almost anything in Act 1 and Act 2.
Capacitor raises your orb slot count. More slots mean more Frost triggers per turn and more room before the queue force-evokes an orb that has not paid off yet. Four or five slots is the goal for a Frost build. Prioritize it in the mid-game.
Shatter changed, and the change favors you. It now evokes every orb in your queue twice, while its direct attack damage dropped to 7 (11 upgraded). For a Frost queue that doubled evoke is a large block burst, since each Frost orb's evoke value (which scales with Focus) fires twice in one action. Hold it for telegraphed heavy turns. Read it as a defensive panic button and a queue reset, not as your kill button.
For where each of these lands relative to the rest of the pool, see the Defect card tier list.
The Damage Outlet (Now Mandatory)
This is the part the old guide treated as optional. Against Aeonglass it is the build.
Lead with the Lightning line. Update 2 leaned hard into it: Tesla Coil now triggers twice per turn instead of once, and the alternate starter relic item:infused-core grants Lightning orbs an extra point of damage. A few Lightning orbs riding alongside your Frost queue turn passive defense into passive offense, scaling on the same Focus you were stacking anyway. That is the cleanest graft because it costs you almost no draft commitment beyond keeping a couple of Lightning sources.
Hyperbeam is the heavier single-card answer, now hitting for 28 (36 upgraded), and it clears the queue while it does. Synthesis and Uproar both got bumped up as well, so the colorless and rare damage options are more viable than they were on the old patch. Whichever you pick, the rule holds: enter Act 3 with a way to deal real damage, or the Wither clock runs you over.
Relic Priorities
Cracked Core comes with every run and channels one free Lightning orb each combat. In a build that now wants Lightning anyway, that free orb stopped being a tax and started being a head start on your offense.
item:ice-cream is the best non-character relic here. Energy that carries between turns lets you bank for the big setup turn where you drop Capacitor, two Defragments, and a pair of Cold Snaps in one round to hit block parity fast.
Mummified Hand gives a free card play whenever you play a Power, and both Defragment and Capacitor are Powers. Play Defragment with it active, then spend the free play on another Power or a Cold Snap for a no-cost Frost channel.
The full relic ranking is in the relic tier list.
Act-by-Act Gameplay
Act 1 is about the foundation. Take every Cold Snap. If Defragment shows up, it is the pick. Capacitor in Act 1 is a strong second. Thin the deck at the merchant so you draw your engine pieces, and grab your first Lightning source so the damage plan has a starting point. By the boss you want two or three Cold Snaps, a Defragment, a Capacitor if offered, and a block floor above the boss's per-turn output.
Act 2 is where the build stabilizes or stalls. The metric is whether passive Frost block exceeds incoming Elite damage. Two Focus and three Frost orbs in a four-slot queue gives 12 passive block, which is short. One more Defragment or a second Glacier tips it. By the Act 2 boss you should generate 20 or more passive block before any card play, with Lightning already chipping in damage each turn.
Act 3 is where the new math bites. Enter with three or four Focus banked, fill the queue with Frost inside two turns, and start applying damage immediately rather than coasting on block. Keep your deck lean so Withers get drawn instead of clogging it, and only let a Wither sit in hand on turns where you have block to spare. Hold Shatter for the boss's big telegraphed swings. Aeonglass hits hard and stacks its Wither clock the longer you take, so win the fight on damage. Out-blocking it is not a plan.
The complete decklist, relic order, and Focus targets for this list are laid out here:
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The Frost Tank still has two genuine weaknesses, and Aeonglass sharpened both.
Fast burst fights punish the setup. If an early Elite or event kills you in two turns, your Frost passive has not come online. Carry one or two early block cards alongside your Frost builders so you survive the turns before the engine takes over.
Stall-punish fights are the new one, and Aeonglass is the headline. A list with no damage outlet cannot out-block Withering Presence forever, because the self-damage and the boss's escalating Strength scale past your block. The answer is not more block. It is committing to a damage win condition early and closing the fight before the clock wins. Build the wall, then make sure the wall can punch.
If you are still learning the orb queue and Focus math, start with the Slay the Spire 2 beginner guide.