When he was healthy, Dante Exum was an X-factor for the Mavericks in the regular season.

At 6'5" with a 6'9" wingspan, he's big for a playmaker. He doesn't hold the ball, pushes the pace a bit and isn't afraid of challenging defensive assignments like either of Jayson Tatum or Jaylen Brown.

But his three-point shot sort of betrayed him in the first three rounds of the playoffs, and coach Jason Kidd clearly lost trust in him.

In the regular season, Exum averaged 19.8 minutes and shot 49.1 percent from deep. Coming into Friday's Game 4, he was at 6.4 minutes with a 26.7 three-point percentage.

But he infused a ton of energy into the Mavericks in Friday's first half. He hit two threes and was plus-15 in just 14 minutes. He had multiple stout defensive possessions on Celtics guards and wings. And if he's back to his regular-season form, he could be a legitimate game-changer.

Prior to the playoffs, Dallas was plus-2.6 points per 100 possessions when Luka played without Exum and plus-16.6 when he played with him. His low-usage, high-effort game looked like a perfect complement to Luka's.

But of course, he's not the only potential swing piece off the bench. A lot of that same praise can be allowed to another Australian, Josh Green, who's even bouncier than Exum.

And of course, there's Dereck Lively II, who's on track to finish the playoffs with more wins over replacement player than anyone in league history's ever piled up in an age-19 (or younger) season.

Lively's relentless activity around the basket led to 11 points and 12 rebounds in 22 minutes. He was plus-20 and hit a three. Seven of those boards were on the offensive end, and those extra possessions were big in demoralizing Boston early on. To this day, offensive rebounding remains one of basketball's most underrated forms of shot creation.

"I think people forget he's a rookie," Luka told reporters after the game. "He's a rookie doing this stuff. He's been amazing the whole season."

As this series goes on, Lively's minutes are likely to keep rising (starting 5 Daniel Gafford only played 10 minutes in Game 4), and Boston doesn't really have anyone to challenge him physically.