Tend the Pests

As an additional cost to cast this spell, sacrifice a creature.
Create X 1/1 black and green Pest creature tokens with "When this token dies, you gain 1 life," where X is the sacrificed creature's power.

Virulent Emissary

Deathtouch
Whenever another creature you control enters, you gain 1 life.

Duskshell Crawler

When this creature enters, put a +1/+1 counter on target creature.
Each creature you control with a +1/+1 counter on it has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.)

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Bogwater Lumaret

Whenever this creature or another creature you control enters, you gain 1 life.

Arachnogenesis

Create X 1/2 green Spider creature tokens with reach, where X is the number of creatures attacking you. Prevent all combat damage that would be dealt this turn by non-Spider creatures.

Pest Mascot

Trample
Whenever you gain life, put a +1/+1 counter on this creature.

Arasta of the Endless Web

Reach
Whenever an opponent casts an instant or sorcery spell, create a 1/2 green Spider creature token with reach.

Haywire Mite

When this creature dies, you gain 2 life.
{G}, Sacrifice this creature: Exile target noncreature artifact or noncreature enchantment.

Cauldron of Essence

Whenever a creature you control dies, each opponent loses 1 life and you gain 1 life.
{1}{B}{G}, {T}, Sacrifice a creature: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

Pest Rescuer

At the beginning of each upkeep, if you don't control a Pest creature token, create a 1/1 black and green Pest creature token with "When this token dies, you gain 1 life."
If you would gain life, you gain that much life plus 1 instead.

Eumidian Terrabotanist

Landfall — Whenever a land you control enters, you gain 1 life.

Pest Infestation

Destroy up to X target artifacts and/or enchantments. Create twice X 1/1 black and green Pest creature tokens with "When this token dies, you gain 1 life."

Twitching Doll

{T}: Add one mana of any color. Put a nest counter on this creature.
{T}, Sacrifice this creature: Create a 2/2 green Spider creature token with reach for each counter on this creature. Activate only as a sorcery.

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Command Tower

Ribtruss Roaster

Devour 1 (As this creature enters, you may sacrifice any number of creatures. This creature enters with that many +1/+1 counters on it.)
At the beginning of your end step, create a number of 1/1 black and green Pest creature tokens equal to the number of +1/+1 counters on this creature. They have "When this token dies, you gain 1 life."

Teacher's Pest

Menace (This creature can't be blocked except by two or more creatures.)
Whenever this creature attacks, you gain 1 life.
{B}{G}: Return this card from your graveyard to the battlefield tapped.

Essence Warden

Whenever another creature enters, you gain 1 life.

Feral Appetite

Attacking Pests you control get +1/+0 and have deathtouch.
{1}{G}: Exile target card from a graveyard. If a creature card is exiled this way, create a 1/1 black and green Pest creature token with "When this token dies, you gain 1 life."

Search for Blex

Look at the top five cards of your library. You may put any number of them into your hand and the rest into your graveyard. You lose 3 life for each card you put into your hand this way.

Blex, Vexing Pest

Other Pests, Bats, Insects, Snakes, and Spiders you control get +1/+1.
When Blex dies, you gain 4 life.

Blex, Vexing Pest // Search for Blex

Starscape Cleric

Offspring {2}{B} (You may pay an additional {2}{B} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
Flying
This creature can't block.
Whenever you gain life, each opponent loses 1 life.

Blech, Loafing Pest

Whenever you gain life, put a +1/+1 counter on each Pest, Bat, Insect, Snake, and Spider you control.

Mirkwood Bats

Flying
Whenever you create or sacrifice a token, each opponent loses 1 life.

Enduring Tenacity

Whenever you gain life, target opponent loses that much life.
When Enduring Tenacity dies, if it was a creature, return it to the battlefield under its owner's control. It's an enchantment. (It's not a creature.)