msem-instigator

Whenever you create one or more tokens, put a +1/+1 counter on target creature you control.
{2}{G}{W}: Create a 0/1 green Plant creature token.

When Bal's Descent enters, each player sacrifices a creature, discards two cards, and mills three cards.
{1}{B}{B}: Transform Bal's Descent. Activate only if your fealty to Swamps is five or greater.

Indestructible
You may play cards from your graveyard.
If you would draw one or more cards, mill that many cards instead.
If a card would be put into your graveyard from anywhere other than your library, exile it instead.

Double strike
Engage (This creature must be blocked each combat if able.)
{1}{R}: Balanced Blade gets +1/+0 until end of turn.

Prowess
Whenever Balefire Conjurer attacks, you may pay {1}{R}. If you do, exile the top card of your library. You may play that card until the end of your next turn.

Menace
As long as Balefire Harbinger is attacking, creatures in its pack can't be blocked unless defending player pays {1} and 1 life for each creature they control that's blocking one of those creatures. (Two or more creatures you control with equal power are in a pack.)

Flying, deathtouch

Whenever Baljurn, the Runelord or another nontoken artifact or enchantment you control enters, create a 0/0 blue Construct artifact creature token. Put a +1/+1 counter on each artifact and/or enchantment creature you control other than Baljurn.

Haste (This creature can attack and {T} as soon as it comes under your control.)
{1}{U}: Balloon Dragoon gains flying until end of turn.

This spell costs {U} less to cast if you dealt combat damage to a player this turn with a Rogue.
Flying
When Balloon Voyager enters, draw a card.

Ward {3} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)
Lifecycle {3} ({3}, Discard this card: Create two tapped 1/1 colorless Elemental creature tokens.)

At the beginning of combat on your turn, if there are five or more creature types among creatures you control, creatures you control get +2/+0 and gain menace until end of turn.

Equipped creature gets +3/+0 and has vigilance.
Equip {3}

Whenever equipped creature attacks, it gains deathtouch until end of turn.
Sacrifice Bandit's Dagger: Target player dealt damage by equipped creature this turn reveals their hand. You choose a nonland card from it. That player discards that card.
Equip {2}

Enchant player
At the beginning of each end step, create X 1/1 green Snake creature tokens, where X is the amount of life enchanted player lost this turn.

Engorge (As this enters, mill three cards, then exile a card from among the milled cards.)
When Bane of Sanity enters, if it engorged a creature card, target player discards two cards.

When Baneblade Stalker enters, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Reach
{4}{B}: Each opponent loses 2 life and you gain 2 life.

Haste
Whenever Banished Companion attacks, it deals 2 damage to you.

When Banished Prophet enters, you may remove a counter from a permanent you control. If you do, put a +1/+1 counter on another target creature you control.

When Banishing Initiate enters, you may exile target nonland permanent you don't control until Banishing Initiate leaves the battlefield.
At the beginning of your end step, sacrifice Banishing Initiate if a card exiled with it has mana value 3 or greater.

Enchant non-Army creature
Enchanted creature can't attack or block.
When Banishment of Aspirations enters, amass Soldiers 1. (Put a +1/+1 counter on an Army you control. It's also a Soldier. If you don't control one, create an 0/0 black Soldier Army creature token first.)

Trample
When Bank Skimmer enters, create a green Aura enchantment token named Turtle's Valor attached to target creature. The token has enchant creature and “Enchanted creature gets +X/+X, where X is its mana value.”

When Banner of Warfare enters, amass Soldiers 1. (Put a +1/+1 counter on an Army you control. It's also a Soldier. If you don't control one, create an 0/0 black Soldier Army creature token first.)
{1}, {T}: Add one mana of any color.

Lifelink
Forestcycling {1}, islandcycling {1} ({1}, Discard this card: Search your libary for a Forest or Island card, reveal it, put it into your hand, then shuffle.)