Ovinomancer

When this creature enters, sacrifice it unless you return three basic lands you control to their owner's hand.
{T}, Return this creature to its owner's hand: Destroy target creature. It can't be regenerated. That creature's controller creates a 0/1 green Sheep creature token.

Akoum Hellkite

Flying
Landfall — Whenever a land you control enters, this creature deals 1 damage to any target. If that land is a Mountain, this creature deals 2 damage instead.

Izzet Boilerworks

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {U}{R}.

Oboro Breezecaller

Flying
{2}, Return a land you control to its owner's hand: Untap target land.

Soratami Mirror-Mage

Flying
{3}, Return three lands you control to their owner's hand: Return target creature to its owner's hand.

Tunneling Geopede

Landfall — Whenever a land you control enters, this creature deals 1 damage to each opponent.

Cosi's Ravager

Landfall — Whenever a land you control enters, you may have this creature deal 1 damage to target player or planeswalker.

Seed the Land

Whenever a land enters, its controller creates a 1/1 green Snake creature token.

Toggo, Goblin Weaponsmith

Landfall — Whenever a land you control enters, create a colorless Equipment artifact token named Rock with "Equipped creature has '{1}, {T}, Sacrifice Rock: This creature deals 2 damage to any target'" and equip {1}.
Partner (You can have two commanders if both have partner.)

Guildless Commons

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {C}{C}.

Uyo, Silent Prophet

Flying
{2}, Return two lands you control to their owner's hand: Copy target instant or sorcery spell. You may choose new targets for the copy.

Hedron Crab

Landfall — Whenever a land you control enters, target player mills three cards. (They put the top three cards of their library into their graveyard.)

Omnath, Locus of Rage

Landfall — Whenever a land you control enters, create a 5/5 red and green Elemental creature token.
Whenever Omnath or another Elemental you control dies, Omnath deals 3 damage to any target.

Valakut Exploration

Landfall — Whenever a land you control enters, exile the top card of your library. You may play that card for as long as it remains exiled.
At the beginning of your end step, if there are cards exiled with this enchantment, put them into their owner's graveyard, then this enchantment deals that much damage to each opponent.

Nesting Dragon

Flying
Landfall — Whenever a land you control enters, create a 0/2 red Dragon Egg creature token with defender and "When this token dies, create a 2/2 red Dragon creature token with flying and '{R}: This token gets +1/+0 until end of turn.'"

Ludevic, Necro-Alchemist

At the beginning of each player's end step, that player may draw a card if a player other than you lost life this turn.
Partner (You can have two commanders if both have partner.)

Gruul Turf

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {R}{G}.

Tireless Tracker

Landfall — Whenever a land you control enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Whenever you sacrifice a Clue, put a +1/+1 counter on this creature.