He gave his men the watchword, “God’s victory”: This clause is very similar to one in 2Macc 8.23. See the comments there.

And with a picked force of the bravest young men, he attacked the king’s pavilion at night and slew as many as two thousand men in the camp: For with a picked force of the bravest young men, Goldstein has “he picked the best of his young men,” which is a more accurate rendering. The word “best” is closer to the Greek than the word bravest. These young soldiers were probably selected not only for their bravery, but for their experience and proven fighting ability. The king’s pavilion is literally “the royal courtyard,” but in this context of a military camp it refers to “the area near the king’s tent” (Good News Bible). Contemporary English Version is similar with “the enemy camp near the king’s tent.”

He stabbed the leading elephant and its rider: Instead of stabbed, the Greek manuscripts say “put together.” Everyone accepts the conjecture stabbed, and so do we since we have no better suggestion. The leading elephant was the one that was put in position to encounter the enemy first during a battle. New Jerusalem Bible, Traduction œcuménique de la Bible, and Abel say “the largest of the elephants,” which is possible, but not likely. Its rider (literally “the one who was in the house,” that is, the howdah on the elephant’s back) does not imply that this man was riding the elephant at the time. The attack was made at night, and the rider would not have been atop the animal at the time. For rider (Good News Bible “keeper”), see the comments on “driver” at 1Macc 6.37.

Here is an alternative model for this verse:

• Then, at night, Judas signaled his men to attack [or, to begin fighting] by saying, “Victory comes from God!” and the best of his young men attacked the area around the king’s tent. They killed at least 2,000 men [in the camp], and stabbed to death* the lead elephant and its trainer.
* Probable text stabbed to death; Greek put together.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.