The Golden Knights score a dynamic two-way winger in Mark Stone and ink him long term. But it cost them key young defenseman Erik Brannstrom.
Golden Knights get: RW Mark Stone, RW Tobias Lindberg
Senators get: D Erik Brannstrom, F Oscar Lindberg, Dallas' 2020 second-round pick

Golden Knights: A
We'll get to the cost in the Ottawa section, but this is an absolutely fantastic addition for the Vegas Golden Knights.
Stone was the most complete winger available at the trade deadline. He's basically Patrice Bergeron but a winger: stellar defensively and a 20-goal scorer every season he's been an NHL regular. Vegas assistant GM Kelly McCrimmon, who had Stone with the Brandon Wheat Kings in junior, knows the player well, and no doubt his presence there was a lure for Stone. (Well, unless he ends up becoming the general manager in Edmonton.)
The right winger slots in perfectly with Jonathan Marchessault and William Karlsson on the Golden Knights' top line, which has faltered this season after dominating in the team's inaugural season. This will allow Reilly Smith to drop down the lineup, perhaps to the team's second line with Max Pacioretty and Paul Stastny. Stone will also bolster the Knights' No. 23-ranked power play (17.1).
The fact that the Knights have agreed to an extension with Stone, according to the player himself, is essential here, too. He's only 26 and has been a steady, consistent player. Owner Bill Foley doesn't want to just challenge for a Stanley Cup after last season's trip to the Final, he wants multiple ones. And obviously, given the $9.5 million that Stone will command annually, it helps that money is no object for the aggressive owner.
The Winnipeg Jets, Nashville Predators and San Jose Sharks all added significant pieces at the trade deadline. Vegas GM George McPhee needed to ante up, and did in an impressive way.

Senators: A-minus
You could hear jaws hitting the floor when Erik Brannstrom's name was announced as being a part of this trade. He's an elite young defenseman, with 28 points in 41 games for the AHL Chicago Wolves. The 19-year-old blueliner was drafted 15th overall in 2017 by Vegas. His offensive game already looks solid, especially as a passer. His defensive game has also looked good and will continue to improve.
Along with Thomas Chabot, the Senators could have two foundational players on the blue line for quite a while.
Center Oscar Lindberg never really found his game in Vegas after a couple of promising seasons with the Rangers before being selected in the expansion draft. He makes $1.7 million against the cap and goes unrestricted this summer.
The second-round pick from Dallas in 2020 gives the Senators three second-rounders next summer.
This grade might be a shade higher had the Senators pulled a first-rounder out the Golden Knights, but perhaps the inclusion of Brannstrom made that impossible. Obviously, the main objective here was to re-sign Stone; since that wasn't going to happen, Senators GM Pierre Dorion pulling a blue-chipper for him is the nearly best-case scenario.