Roil Elemental — ruling 1

A landfall ability triggers whenever a land you control enters for any reason. It triggers whenever you play a land, as well as whenever a spell or ability puts a land onto the battlefield under your control.

Roil Elemental — ruling 2

A landfall ability doesn't trigger if a permanent already on the battlefield becomes a land.

Roil Elemental — ruling 3

Whenever a land you control enters, each landfall ability of the permanents you control will trigger. You can put them on the stack in any order. The last ability you put on the stack will be the first one to resolve (As a result, you can have those abilities resolve in the order of your choosing.).

Roil Elemental — ruling 4

If Roil Elemental leaves the battlefield, you no longer control it, so all of its control-change effects end.

Roil Elemental — ruling 5

If Roil Elemental ceases to be under your control before its ability resolves, you won't gain control of the targeted creature at all.

Roil Elemental — ruling 6

You may target a creature you already control with Roil Elemental's ability. This will usually have no visible effect, but it will overwrite any previous control-change effects. For example, if you gain control of Roil Elemental until the end of the turn (with Mark of Mutiny, perhaps), then its landfall ability triggers and you target Roil Elemental itself, you'll gain control of it indefinitely (since its control-change effect will last for as long as you control it).

Roil Elemental : règles, fonctionnement et interactions (MTG)

Roil Elemental is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flying Landfall — Whenever a land you control enters, you may gain control of target creature for as long as you control this creature.

How it works : Roil Elemental

Original English text — Wizards of the Coast / Scryfall

#1November 8, 2024· Wizards of the Coast
A landfall ability triggers whenever a land you control enters for any reason. It triggers whenever you play a land, as well as whenever a spell or ability puts a land onto the battlefield under your control.
No other card is named in this ruling.
#2November 8, 2024· Wizards of the Coast
A landfall ability doesn't trigger if a permanent already on the battlefield becomes a land.
No other card is named in this ruling.
#3November 8, 2024· Wizards of the Coast
Whenever a land you control enters, each landfall ability of the permanents you control will trigger. You can put them on the stack in any order. The last ability you put on the stack will be the first one to resolve (As a result, you can have those abilities resolve in the order of your choosing.).
No other card is named in this ruling.
#4October 1, 2009· Wizards of the Coast
If Roil Elemental leaves the battlefield, you no longer control it, so all of its control-change effects end.
No other card is named in this ruling.
#5October 1, 2009· Wizards of the Coast
If Roil Elemental ceases to be under your control before its ability resolves, you won't gain control of the targeted creature at all.
No other card is named in this ruling.
#6October 1, 2009· Wizards of the Coast
You may target a creature you already control with Roil Elemental's ability. This will usually have no visible effect, but it will overwrite any previous control-change effects. For example, if you gain control of Roil Elemental until the end of the turn (with Mark of Mutiny, perhaps), then its landfall ability triggers and you target Roil Elemental itself, you'll gain control of it indefinitely (since its control-change effect will last for as long as you control it).
No other card is named in this ruling.