Bellowing Elk — ruling 1

Bellowing Elk’s effect checks each turn whether it applies during that turn. It doesn’t check only during the turn it enters the battlefield.

Bellowing Elk — ruling 2

Bellowing Elk’s effect applies even if the other creature entered the battlefield under your control before Bellowing Elk entered the battlefield, and it continues to apply even if that creature leaves the battlefield.

Bellowing Elk : règles, fonctionnement et interactions (MTG)

Bellowing Elk 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

As long as you had another creature enter the battlefield under your control this turn, this creature has trample and indestructible.

How it works : Bellowing Elk

Original English text — Wizards of the Coast / Scryfall

#1June 14, 2019· Wizards of the Coast
Bellowing Elk’s effect checks each turn whether it applies during that turn. It doesn’t check only during the turn it enters the battlefield.
No other card is named in this ruling.
#2June 14, 2019· Wizards of the Coast
Bellowing Elk’s effect applies even if the other creature entered the battlefield under your control before Bellowing Elk entered the battlefield, and it continues to apply even if that creature leaves the battlefield.
No other card is named in this ruling.