Krenko, Tin Street Kingpin

Whenever Krenko attacks, put a +1/+1 counter on it, then create a number of 1/1 red Goblin creature tokens equal to Krenko's power.

Combat Celebrant

If this creature hasn't been exerted this turn, you may exert it as it attacks. When you do, untap all other creatures you control and after this phase, there is an additional combat phase. (An exerted creature won't untap during your next untap step.)

Securitron Squadron

Squad {3} (As an additional cost to cast this spell, you may pay {3} any number of times. When this creature enters, create that many tokens that are copies of it.)
Vigilance
Whenever a creature token you control enters, put a +1/+1 counter on it.

Anim Pakal, Thousandth Moon

Whenever you attack with one or more non-Gnome creatures, put a +1/+1 counter on Anim Pakal, then create X 1/1 colorless Gnome artifact creature tokens that are tapped and attacking, where X is the number of +1/+1 counters on Anim Pakal.

Kinscaer Sentry

First strike, lifelink
Whenever this creature attacks, you may put a creature card with mana value X or less from your hand onto the battlefield tapped and attacking, where X is the number of attacking creatures you control.

Raph & Leo, Sibling Rivals

Whenever Raph & Leo attack, if it's the first combat phase of the turn, untap one or two target attacking creatures. After this phase, there is an additional combat phase.

Fear of Missing Out

When this creature enters, discard a card, then draw a card.
Delirium — Whenever this creature attacks for the first time each turn, if there are four or more card types among cards in your graveyard, untap target creature. After this phase, there is an additional combat phase.

Phelia, Exuberant Shepherd

Flash
Whenever Phelia attacks, exile up to one other target nonland permanent. At the beginning of the next end step, return that card to the battlefield under its owner's control. If it entered under your control, put a +1/+1 counter on Phelia.

Arabella, Abandoned Doll

Whenever Arabella attacks, it deals X damage to each opponent and you gain X life, where X is the number of creatures you control with power 2 or less.

Guide of Souls

Whenever another creature you control enters, you gain 1 life and get {E} (an energy counter).
Whenever you attack, you may pay {E}{E}{E}. When you do, put two +1/+1 counters and a flying counter on target attacking creature. It becomes an Angel in addition to its other types.