Heroic Reinforcements — ruling 1

The second part of Heroic Reinforcements's effect affects only creatures you control at the time it's applied, including the tokens created by the first part of its effect. Creatures you begin to control later in the turn won't get +1/+1 or gain haste.

Heroic Reinforcements : règles, fonctionnement et interactions (MTG)

Heroic Reinforcements 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

Create two 1/1 white Soldier creature tokens. Until end of turn, creatures you control get +1/+1 and gain haste. (They can attack and this turn.)

How it works : Heroic Reinforcements

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2018· Wizards of the Coast
The second part of Heroic Reinforcements's effect affects only creatures you control at the time it's applied, including the tokens created by the first part of its effect. Creatures you begin to control later in the turn won't get +1/+1 or gain haste.
No other card is named in this ruling.