Isaac CodexOnly one safe purchase? Brimstone is the clearer pick when you need a charged shot to pass through enemies and obstacles along a line. Mom’s Knife rewards a different rhythm: hold the knife against a target for repeated hits, or charge and throw it farther. Both need aiming. In Repentance, buying both gives you the knife plus an extra knife barrage, not a normal Brimstone beam alongside it. Check the price and your health after paying before choosing either.
Check the hearts first
Look at each pedestal’s current price, then count the hearts you will still have. Devil Deals can charge red containers or Soul Hearts, and the price can change with your health and character. Spending your last red container need not kill you if Soul or Black Hearts remain; having no health left is a different risk. If you cannot see a way to survive the purchase and the next room, leave the deal. Do not use the screenshot’s HUD as a fixed price or a safe-health example.
Which attack fits this run?
| What matters right now | What the items actually give you |
|---|---|
| Enemies line up or hide behind obstacles | Brimstone: a charged beam pierces enemies and passes through obstacles. You can aim through a line instead of reaching each target with the knife. |
| You can hold position near a target, or time a throw | Mom's Knife: contact can hit repeatedly while held; charging increases a thrown knife's reach. In Repentance, peak throw damage arrives before full charge, so longer charge is mainly for range. |
| Tech X is already in the build | Different pairings, no automatic winner: Brimstone makes a larger Brimstone ring; Mom's Knife travels with a Tech X ring when thrown in Repentance. Pick the pattern you can actually use. |
| You can pay for both | Repentance: Mom's Knife takes priority. Throwing it adds more knives, and longer charges add to the barrage. You gain the combo, but give up the ordinary Brimstone beam as your main shot. |
The first two rows are about where you can deal damage, not a promise that one item always has higher damage. If this run already depends on another attack interaction, check that interaction before spending hearts.
The exception worth remembering
The extra Brimstone-and-Knife barrage above does not apply to Azazel’s starting short-range beam. The ring and barrage descriptions here come from the cached Repentance entries; older editions can behave differently. If your run turns on a special character or a three-item combination, do not treat the pairwise Tech X rows as a tested result for all three together.
Sources
Mechanics are adapted from The Binding of Isaac: Rebirth Wiki (wiki.gg) contributors’ Brimstone revision 265889, Mom’s Knife revision 266875, and Devil Room revision 269024, saved 10 September 2026. A newer live revision was not verified. The conditional picks and “leave the deal” advice are editorial interpretation. The owner’s screenshot illustrates the choice; it is not a test of the items or their outcome.
This adaptation of the wiki contributors’ text is licensed CC BY-SA 4.0. Game artwork rights are separate from the owner’s capture.