Den of the Bugbear

If you control two or more other lands, Den of the Bugbear enters tapped.
{T}: Add {R}.
{3}{R}: Until end of turn, Den of the Bugbear becomes a 3/2 red Goblin creature with "Whenever this creature attacks, create a 1/1 red Goblin creature token that's tapped and attacking." It's still a land.

Volo, Guide to Monsters

Whenever you cast a creature spell that doesn't share a creature type with a creature you control or a creature card in your graveyard, copy that spell. (A copy of a creature spell becomes a token.)

Neverwinter Dryad

{2}, Sacrifice Neverwinter Dryad: Search your library for a basic Forest card, put it onto the battlefield tapped, then shuffle.

Mordenkainen's Polymorph

Until end of turn, target creature becomes a Dragon with base power and toughness 4/4 and gains flying. (It loses all other creature types.)

Plains

Devoted Paladin

Beacon of Hope — When Devoted Paladin enters, creatures you control get +1/+1 and gain vigilance until end of turn.

Feywild Trickster

Whenever you roll one or more dice, create a 1/1 blue Faerie Dragon creature token with flying.

+2 Mace

Equipped creature gets +2/+2.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Hill Giant Herdgorger

When Hill Giant Herdgorger enters, you gain 3 life.

Wandering Troubadour

At the beginning of your end step, if you had a land enter the battlefield under your control this turn, venture into the dungeon. (Enter the first room or advance to the next room.)

Air-Cult Elemental

Flying
Whirlwind — When Air-Cult Elemental enters, return up to one other target creature to its owner's hand.

Moon-Blessed Cleric

Divine Intervention — When Moon-Blessed Cleric enters, you may search your library for an enchantment card, reveal it, then shuffle and put that card on top.

Sepulcher Ghoul

Sacrifice another creature: Sepulcher Ghoul gets +2/+2 until end of turn. Activate only once each turn.

Faerie Dragon

Hobgoblin Captain

Pack tactics — Whenever Hobgoblin Captain attacks, if you attacked with creatures with total power 6 or greater this combat, Hobgoblin Captain gains first strike until end of turn.

Boots of Speed

Equipped creature gets +1/+0 and has haste.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)