Flash Thompson, Spider-Fan

Flash
When Flash Thompson enters, choose one or both —
• Heckle — Tap target creature.
• Hero Worship — Untap target creature.

Anti-Venom, Horrifying Healer

When Anti-Venom enters, if he was cast, return target creature card from your graveyard to the battlefield.
If damage would be dealt to Anti-Venom, prevent that damage and put that many +1/+1 counters on him.

Aunt May

Whenever another creature you control enters, you gain 1 life. If it's a Spider, put a +1/+1 counter on it.

Maximum Carnage

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Until your next turn, each creature attacks each combat if able and attacks a player other than you if able.
II — Add {R}{R}{R}.
III — This Saga deals 5 damage to each opponent.

Spider-Byte, Web Warden

When Spider-Byte enters, return up to one target nonland permanent to its owner's hand.

Spider-UK

Web-slinging {2}{W} (You may cast this spell for {2}{W} if you also return a tapped creature you control to its owner's hand.)
At the beginning of your end step, if two or more creatures entered the battlefield under your control this turn, you draw a card and gain 2 life.

Beetle, Legacy Criminal

Flying
{1}{U}, Exile this card from your graveyard: Put a +1/+1 counter on target creature. It gains flying until end of turn. Activate only as a sorcery.

Shocker, Unshakable

During your turn, Shocker has first strike.
Vibro-Shock Gauntlets — When Shocker enters, he deals 2 damage to target creature and 2 damage to that creature's controller.

Doc Ock, Sinister Scientist

As long as there are eight or more cards in your graveyard, Doc Ock has base power and toughness 8/8.
As long as you control another Villain, Doc Ock has hexproof. (He can't be the target of spells or abilities your opponents control.)

Kraven the Hunter

Trample
Whenever a creature an opponent controls with the greatest power among creatures that player controls dies, draw a card and put a +1/+1 counter on Kraven the Hunter.

Black Cat, Cunning Thief

When Black Cat enters, look at the top nine cards of target opponent's library, exile two of them face down, then put the rest on the bottom of their library in a random order. You may play the exiled cards for as long as they remain exiled. Mana of any type can be spent to cast spells this way.

Mary Jane Watson

Whenever a Spider you control enters, draw a card. This ability triggers only once each turn.

Rhino, Barreling Brute

Vigilance, trample, haste
Whenever Rhino attacks, if you've cast a spell with mana value 4 or greater this turn, draw a card.

Spider-Man, Brooklyn Visionary

Web-slinging {2}{G} (You may cast this spell for {2}{G} if you also return a tapped creature you control to its owner's hand.)
When Spider-Man enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Lizard, Connors's Curse

Trample
Lizard Formula — When Lizard, Connors's Curse enters, up to one other target creature loses all abilities and becomes a green Lizard creature with base power and toughness 4/4.

J. Jonah Jameson

When J. Jonah Jameson enters, suspect up to one target creature. (A suspected creature has menace and can't block.)
Whenever a creature you control with menace attacks, create a Treasure token.

Hydro-Man, Fluid Felon

Whenever you cast a blue spell, if Hydro-Man is a creature, he gets +1/+1 until end of turn.
At the beginning of your end step, untap Hydro-Man. Until your next turn, he becomes a land and gains "{T}: Add {U}." (He's not a creature during that time.)

Spider-Man, Web-Slinger

Web-slinging {W} (You may cast this spell for {W} if you also return a tapped creature you control to its owner's hand.)