Cheapest priced copy (Commander Legends: Battle for Baldur's Gate): $0.79 at Card Kingdom, near mint, their price list as of .
Mizzium Mortars 
Sorcery · Rare · Return to Ravnica · #101
Mizzium Mortars deals 4 damage to target creature you don't control.
Overload {3}{R}{R}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.79 to $4.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2015 | 163 | Rare | $0.99 | — |
| Commander Legends: Battle for Baldur's Gate | 803 | Rare | $0.79 | — |
| GRN Guild Kit | 32 | Rare | $0.79 | — |
| Modern Masters 2017 | 101 | Rare | $0.79 | $3.49 |
| Return to Ravnica | 101 | Rare | $0.79 | $4.99 |
| Secret Lair Drop (The Rage of Yian Garuga) | 2249 | Rare | — | — |
5 rulings from Wizards of the Coast
- 12 January 2024To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an overload cost), add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
- 12 January 2024If you don't pay the overload cost of a spell with overload, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.
- 12 January 2024Note that if the spell with overload is dealing damage, protection from that spell's color will still prevent that damage.
- 12 January 2024Because a spell with overload doesn't target when its overload cost is paid, it may affect permanents with hexproof or with protection from the appropriate color.
- 12 January 2024If you are instructed to cast a spell with overload "without paying its mana cost," you can't choose to pay its overload cost instead.