A category specialist isn't for everyone. You are always better off, in a general sense, to have a player on your team that has a higher fantasy value and contributes in multiple categories.
That said, there is a place on rosters, especially during short, calculated stretches, for a player who only really contributes in one key category. The key to rostering such a player is making sure you do so without hurting yourself elsewhere.
How that works is specific to your league settings. In weekly leagues, it could mean bringing the specialist in when his team has a four-game week on tap and one of your fringe players is only playing twice. In rotisserie leagues with game limits it might mean stashing the specialist on your bench for when one of your players is day-to-day. In head-to-head formats it could mean looking at your weekly opponent's strengths and weaknesses and specifically targeting them with a specialist in those categories. But it doesn't have to be that much work. It can simply be glancing at the roto categories and seeing where you could gain a point or two with a boost, or it could be a matter of tracking which category you often lose by a slim margin.
You also have to take careful note where a specialist might hurt your other categories. Collateral damage is inevitable with most category-specific players because they'd be no-brainer fantasy acquisitions if they were okay across all categories. How to use these players is definitely specific to your league.
With that in mind, here are a few available category specialists for your fantasy teams.
Plus/minus
Adrian Kempe, RW, Los Angeles Kings (rostered in 28.7 percent of ESPN leagues)
Tied for 13th in the NHL with 13 points at five-on-five hockey this season, Kempe, Tyler Toffoli and Tanner Pearson have proven to be a quality trio in the absence of Jeff Carter. The line has accounted for 10 goals at even strength while allowing only two, explaining Kempe's plus-12 this season. Whether or not they stick together after Carter returns later this season (possibly early 2018) is a bridge to cross when we get there.
Anton Stralman, D, Tampa Bay Lightning (21.9 percent)
With the advantage of being on the ice for about 40 percent of Steven Stamkos' and Nikita Kucherov's total ice time at even strength this season, Stralman paces the NHL with a plus-16 (matched only by Auston Matthews). He's playing a reduced role with the continued emergence of Mikhail Sergachev on the power play, so he takes a hit in power-play points, but Stralman isn't really fantasy dead weight in any category.
Brian Gibbons, C, New Jersey Devils (12.4 percent)
The Devils' fourth line is getting some great matchups to do some offensive damage so far this season. Playing with rookie Blake Coleman and Stefan Noesen, Gibbons has managed too score nine goals and sits at plus-12. His current line has scored five goals together and only allowed one against. They will play minimal ice time and will be streaky at best, but Gibbons could provide a healthy little boost on the right week.
Penalty minutes
Derek Dorsett, RW, Vancouver Canucks (22.6 percent)
Try to ignore the seven goals this season, as they are definitely out of character for the rough-and-tumble Dorsett. He leads the league in PIM and is on pace for more than 300 minutes by the end of the season. While he's more likely to finish with fewer than 200, he's a good candidate to lead the NHL in the category and help boost your fantasy team along the way. Again, just don't count on contributions in other categories, as his pace for goals has zero chance of sustainability with a 26.9 shooting percentage this season compared to a nine-year career shooting percentage of 7.3.
Antoine Roussel, LW, Dallas Stars (10.3 percent)
Roussel has a knack for finding himself on a scoring line for short bursts, as he did on Saturday against the Edmonton Oilers. Five of his six points, in fact, have come in two games this season. However, he's usually busy racking up time in the sin bin. He's finished with more than 100 PIM in each of the past four seasons, including last season when he missed 22 games. Roussel comes with the added bonus of coming close to 30 points every season, thanks to his occasional ice time with Jamie Benn or Tyler Seguin (or both).
Shots on goal
Rick Nash, LW/RW, New York Rangers (38.0 percent)
Tied for 10th in the league with 72 shots on goal this season, Nash isn't nearly as much of a fantasy dud as his representation on only 38 percent of rosters might suggest. In fact, he's on pace for 27 goals despite his shooting percentage (9.2 percent) still hanging out well below his career average (12.2 percent).
Power-play points
Mikko Rantanen, RW, Colorado Avalanche (50.8 percent)
Currently tied for fifth in the NHL with 10 power-play points, Rantanen is on pace for 73 points this season and is available in half of ESPN leagues. His plus/minus is a pitfall, but it's clear that this sophomore is growing into his top-line role with Nathan MacKinnon, both on and off the power play. He should probably be on more rosters based on his overall merits, not just as a power-play specialist.
Forwards on the move
Teuvo Teravainen, LW, Carolina Hurricanes (up 62 spots to No. 142)
There it is! A small tweak to the Hurricanes' top line, switching out Elias Lindholm for Teravainen, has meant an offensive explosion for Jordan Staal, Sebastian Aho and, of course, Teravainen. The trio have collectively accounted for 29 points in seven games since coming together.
Matt Duchene, C, Ottawa Senators (down 10 spots to No. 148)
The grass isn't always greener on the other side. Duchene's life as a Senator hasn't gotten off to a rousing start. Through five games, he's pointless (minus-6). The Sens have been toying with different combinations for him with little luck so far. Without an offensive boost soon, Duchene could find himself on the third line (which isn't as bad as most third lines, as the Senators like to spread things out -- just ask Mike Hoffman).
Mitch Marner, C/RW, Toronto Maple Leafs (up 33 spots to No. 139)
Sometimes the doghouse can be a shortcut to better things. After being relegated to the fourth line for a stretch, Marner clawed his way back to what is arguably the Leafs' second line. He was helped along the way by an injury to Auston Matthews that forced coach Mike Babcock's hand, but fantasy players will take it. Marner was spotted on Saturday playing with Tyler Bozak (another recent doghouse resident) and James van Riemsdyk to the tune of two assists. It brings Marner to nine points in November, which is already three more than he had in October.
Defensemen on the move
Oliver Ekman-Larsson, D, Arizona Coyotes (down 18 spots to No. 158)
I know I'm still moving him down the rankings here, but I do still believe that OEL can turn this thing around. When we checked in on Ekman-Larsson in this space a month ago, he was on pace for a minus-92 rating and only 164 shots on goal. Those have "improved" to a pace for a minus-56 rating and 224 shots on goal, which means Ekman-Larsson has made some marginal improvements over the past month. That is shown on the ESPN Player Rater where, instead off outside the realm of roster worthiness, Ekman-Larsson sits at 28th among defensemen over the past 30 days. He's eating up big minutes and continuing to shoot the puck. Don't give up on him yet.
Goaltenders on the move
Cam Talbot, G, Edmonton Oilers (down 27 spots to No. 106)
While others have defined a quality start in the NHL under different measures, I like to consider a "fantasy quality start" to be any game with two or fewer goals or three or fewer goals plus a win. By that measuring stick, Talbot has made eight fantasy quality starts in 18 chances this season, which is far below what we expect from a No. 1 fantasy goaltender.
Quick hits
Arizona's Clayton Keller was admittedly cold for three games prior to being separated from Max Domi and Derek Stepan, but the separation hasn't helped heat him up. He has one point going back six games and looks to be pushing through his first rookie slump. ... Nothing to get excited about after just one game, but Drake Caggiula got to play with Connor McDavid on Saturday as the Oilers fiddle with line combinations. The result was two goals. More than anything else, this shows a new willingness to play with McDavid's linemates, and the situation should be monitored closely for the coming week. ... For a fourth-string goaltender, Maxime Lagace has been pretty darn good for the Vegas Golden Knights. But with Malcolm Subban back to health, one has to expect the original backup will be back at the helm until Marc-Andre Fleury returns.