Effect: Crits have a 50% chance to explode, dealing 50% of the triggering crit's damage to nearby enemies. First copy only: +2% Crit Chance. Radius scales with copies and Size stat at pickup (max 8.0, min 1.0).
Unlock: Kill 3,000 enemies with the Sniper Rifle
Grandma's Secret Tonic is an Epic item that gives each critical hit a 50% chance to create a pink explosion at the hit enemy's position. All enemies within the explosion radius take damage equal to 50% of the original crit damage. The proc chance and explosion damage multiplier are fixed - they do not change no matter how many copies you hold. The first copy also grants +2% Crit Chance, but additional copies do not add more Crit Chance.
The explosion damage formula is: ExplosionDamage = 0.5 x CritDamage. Since the explosion deals half of a crit, which itself deals double normal damage, a triggering explosion effectively deals the same damage as a normal (non-crit) hit to all enemies in range. Against packed groups this means every crit that triggers effectively hits nearby enemies for free at standard damage.
Proc chance is always 50% and explosion damage is always 50% of crit damage regardless of copy count. The only thing additional copies add is explosion radius, which caps at 8.0 and is reached at either 5 copies at 1.0x Size or just 1 copy at 2.0x Size. The wiki explicitly advises saving a Banish for Grandma's Secret Tonic in long runs once it stops providing value - usually after 2 to 5 copies depending on your Size investment.
The radius formula is: min(max((3 + n) x S, 1.0), 8.0) where n is the number of copies and S is your Size multiplier. Both the number of copies and the Size stat are snapshotted at the moment you pick up each copy. Gaining Size after picking up Grandma's Secret Tonic does not update the radius until you pick up the next copy.
| Copies | Radius at 1.0x Size | Radius at 1.5x Size | Radius at 2.0x Size |
|---|---|---|---|
| 1 | 4.0 | 6.0 | 8.0 (capped) |
| 2 | 5.0 | 7.5 | 8.0 (capped) |
| 3 | 6.0 | 8.0 (capped) | 8.0 (capped) |
| 5 | 8.0 (capped) | 8.0 (capped) | 8.0 (capped) |
Because radius is recalculated at pickup, you can reach the maximum radius with fewer copies if you are already at 2.0x Size when you pick them up. A single copy picked up at 2.0x Size gives the same radius as 5 copies at 1.0x Size. Noelle's passive (+Size per level) and Size Tome make it realistic to reach 1.5-2.0x Size mid-run, significantly reducing how many copies you need before Grandma's Secret Tonic is fully capped and safe to banish.
Kill 3,000 enemies with the Sniper Rifle across any number of runs. The Sniper Rifle is a precision weapon that deals high single-target damage, making it slower to accumulate kills than area weapons. Pair it with high-density enemy stages (Cursed Tome helps), Precision Tome to increase crit rate so each shot does more damage, and Quantity Tome to fire more rounds per cycle. After meeting the condition, purchase Grandma's Secret Tonic from the Unlocks shop with Silver.
CL4NK - The wiki names CL4NK directly as the primary character for Grandma's Secret Tonic. His Crit Happens passive grants +1% Crit Chance per level, meaning by Level 30 he has 30% passive crit on top of any Precision Tome investment. At high crit rates, every explosion from Grandma's Secret Tonic fires frequently enough to provide meaningful crowd clear supplementing his Revolver and Bone projectiles. The wiki's crit build core is Precision Tome + Giant Fork + Grandma's Secret Tonic + Forbidden Juice - CL4NK is the character that makes all four pieces work simultaneously.
Bush - Bush's passive gives bonus damage on crits, making him a natural crit-oriented character alongside CL4NK. The Screen Rant character build guide confirms Bush wants Precision Tome and Quantity Tome as core picks, which are the same tomes that enable Grandma's Secret Tonic to fire consistently. Bush's Sniper Rifle is also the weapon required to unlock Grandma's Secret Tonic - grinding the unlock naturally on Bush means the item arrives in his pool at the same time his kill count with the Sniper Rifle completes.
Noelle - Noelle's passive grants +Size and +Damage per level, making her the best character for reaching high Size values. As established above, a higher Size multiplier at pickup means fewer copies of Grandma's Secret Tonic are needed to reach the maximum explosion radius. With Noelle at 2.0x Size, a single copy already hits the radius cap. Her builds from Twinfinite's best build guide run Chaos, XP, Cursed, and Precision Tomes, with Precision providing the crit rate that feeds Grandma's Secret Tonic's explosions.
On each critical hit, there is a 50% chance to create a pink explosion at the enemy's position dealing 50% of the crit's damage to all enemies in radius. The first copy grants +2% Crit Chance; additional copies do not. Proc chance and explosion damage are always fixed at 50%. Additional copies only increase explosion radius, which caps at 8.0. Overpowered Lamp gives an extra explosion proc roll.
Kill 3,000 enemies with the Sniper Rifle across any number of runs. After meeting the condition, purchase Grandma's Secret Tonic from the Unlocks shop with Silver.
No. Proc chance is always 50% and explosion damage is always 50% of crit damage regardless of how many copies you hold. Additional copies only increase the explosion radius, which caps at 8.0 (reached at 5 copies at 1.0x Size or 1 copy at 2.0x Size). The wiki advises banishing Grandma's Secret Tonic in long runs once the radius is capped.
Yes - this is explicitly confirmed by the wiki, and is a notable exception because Overpowered Lamp does NOT work with the other crit synergy items Demonic Blade and Giant Fork. With Overpowered Lamp, each crit gets a second independent 50% roll for the explosion, effectively raising the total chance to around 75%.
