There is no shortage of removal spells that have been released over Magic: The Gathering's long history. Removal spells are cards that can destroy or otherwise remove a creature from the opponent's field. They have become staples, with multiple removal spells tending to release in each set at just about every rarity.
This is especially nice for Pauper. Pauper is Magic: The Gathering's all-common format; so long as a card was released at the common rarity at any point, it is usable (excluding acorn-stamped and cards illegal in constructed play). This makes the card pool for Pauper incredibly large, and has led to it having its fair share of powerful removal spells you should have on your radar.
10 You Are Already Dead
Generally, removal spells have a one-to-one cost, meaning that while the opponent loses their creature, you lose a card out of your hand to maintain an equal loss of card advantage. However, You Are Already Dead will also let you draw a card while destroying a creature.
It does come with a stipulation, as You Are Already Dead can only destroy a creature that was dealt damage. However, this makes any creature that blocks at risk, just by having You Are Already Dead in your hand. It only costs one mana as well, making it trivial to keep mana up to be able to cast it.
9 Vendetta
One-mana removal spells are generally always going to be among the best. As such, Vendetta slots great in the sideboard to bring out against any deck that is not running any black creatures.
For one mana, Vendetta can destroy any nonblack creature while preventing it from being able to be regenerated. It does come with a cost of losing life equal to the destroyed creature's toughness, however. Regardless, this is hardly a downside, as removing a key creature your opponent controls is much more important than your life total.
8 Ghastly Demise
Ghastly Demise is a fantastic removal spell for decks that put a lot of cards into their graveyard, such as Reanimator. Ghastly Demise can destroy any non-black creature with toughness equal to the number of cards in your graveyard.
Since Ghastly Demise only costs one mana, it's rather easy to cast. It can easily destroy low-mana creatures, as you'll likely be loading up the graveyard with a few spells at the start of the game. Ghastly Demise generally only gets better as the game progresses, as the number of cards in your graveyard will only grow.
7 Bone Shards
Bone Shards can destroy any creature or planeswalker at the cost of sacrificing a creature or discarding a card, which is hardly a downside for graveyard decks that want to put things there anyway.
While it is a sorcery speed removal, the low mana cost of Bone Shards is generally why you want to play it. In decks that run cards with madness, or Reanimator decks aiming to bring things back, getting them out of your hand is exactly what you want to be doing.
6 Terminate
Of the few Pauper multi-colored removal spells, Terminate is the best of the lot. It's easy to cast, costs only one red and one black to cast, and can be easily done in any Rakdos (red/black) deck.
Terminate can simply destroy any creature at instant speed while preventing it from being regenerated. It's a staple removal spell in the colors, and with more powerful Rakdos strategies rising, Terminate is among the best choices to play inside of that core. While it does cost two mana, its flexibility with no downside to you is what makes it so strong.
5 Doom Blade
Doom Blade is one of the most iconic removal spells, and for Pauper, a staple against decks that do not run any black creatures. For two mana, Doom Blade can destroy any nonblack creature for no extra downside at instant speed.
Doom Blade has no other restrictions or costs, which is what makes it so powerful. Pauper doesn't have too many strong black creatures compared to the other colors, meaning Doom Blade can hit most of the top creatures in the metagame.
4 Feed The Swarm
Feed The Swarm is one of the select few cards in monoblack that can destroy an enchantment (in fact, Ghastly Death Tyrant is the only other card that can) in the entire game, not just Pauper.
It's a staple in black decks, since it can hit both creatures and enchantments, giving it a versatility that no other removal spell has. It does also require you to lose life equal to the mana value of the permanent destroyed, but it's a small price to pay for removing a key card from play.
3 Chainer's Edict
Though not a traditional removal spell, Chainer's Edict is such a powerful removal spell that almost every black deck finds space for it. For two mana, Chainer's Edict forces the opponent to sacrifice a creature, and comes with flashback for seven mana, which helps it to close out games that drag on.
Many top Pauper decks don't play many creatures, which allows for Chainer's Edict to hit the creatures that matter. As it forces a sacrifice rather than destroys or targets anything, it can also hit hexproof and indestructible creatures should the need arise.
2 Snuff Out
Snuff Out is a removal spell that can destroy any nonblack creature and prevent it from being regenerated. While it technically costs four mana to play, odds are you'll never actually be paying mana to play it.
There is an alternate cost if you control a Swamp, allowing you to pay four life instead of three generic and one black. Pauper has very few free spells like this, making Snuff Out a staple removal card in any deck that plays any form of Swamp.
1 Cast Down
Cast Down is a staple for Pauper removal because it hits any nonlegendary creature, which is just about every creature in the format.
There are only 12 legendary creature cards legal in the format (and all but three of them are creatures with no abilities), and none of these cards are played in any serious capacity. Cast Down hits more creatures than almost any other removal spell in the format, all while having the easiest casting requirements at just one generic and one black mana.