Lantern Scout — ruling 1

Multiple instances of lifelink on the same creature are redundant. There usually isn't much benefit in having the rally ability resolve more than once in a turn, other than that new creatures will be affected by the ability resolving an additional time.

Lantern Scout — ruling 2

When an Ally enters the battlefield under your control, each rally 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.

Lantern Scout — ruling 3

If a creature with a rally ability enters the battlefield under your control at the same time as other Allies, that ability will trigger once for each of those creatures and once for the creature with the ability itself.

Lantern Scout : règles, fonctionnement et interactions (MTG)

Lantern Scout 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

Rally — Whenever this creature or another Ally you control enters, creatures you control gain lifelink until end of turn.

How it works : Lantern Scout

Original English text — Wizards of the Coast / Scryfall

#1August 25, 2015· Wizards of the Coast
Multiple instances of lifelink on the same creature are redundant. There usually isn't much benefit in having the rally ability resolve more than once in a turn, other than that new creatures will be affected by the ability resolving an additional time.
No other card is named in this ruling.
#2August 25, 2015· Wizards of the Coast
When an Ally enters the battlefield under your control, each rally 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.
No other card is named in this ruling.
#3August 25, 2015· Wizards of the Coast
If a creature with a rally ability enters the battlefield under your control at the same time as other Allies, that ability will trigger once for each of those creatures and once for the creature with the ability itself.
No other card is named in this ruling.