Saddled Rimestag’s effect checks each turn whether it applies during that turn. It doesn’t check only during the turn it enters the battlefield.
14-06-2019
wotc
Saddled Rimestag’s effect applies even if the other creature entered the battlefield under your control before Saddled Rimestag entered the battlefield, and it continues to apply even if that creature leaves the battlefield.
14-06-2019
wotc
Saddled Rimestag doesn’t get more than +2/+2 if you had more than one other creature enter the battlefield under your control during a turn.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.