They are carnival rides, these Manchester United and Liverpool teams in a season unlike few others in the Premier League.
Careening wildly from one extreme to the other, lurching from side to side or ascending the highest of peaks before rapidly plummeting to the lowest of valleys. They provide thrills of excitement, chills of despair and the occasional moment of stomach churn as each shock moment hits.
There's no need for a yardbarker to promote the 100th meeting at Anfield between these two cherished rivals given their extreme fluctuations heading into Sunday's encounter, but carrying an antacid or a flask to allay the nerves is advisable.
Both teams currently find themselves on the outside looking in for European play next season, though they have reached the knockout round of the current Europa League tournament. Sixth-place Manchester United (9-7-5) entered that fray due to their Champions League failings, while Liverpool (8-7-6) - three points behind the Red Devils in eighth - scraped by directly with play just good enough not to lose.
For United, the past seven weeks of league play have been akin to a rollercoaster's lengthiest descent from the highest peak.
When they defend well, they don't score. When they do score goals, defence becomes an afterthought. As a result, Louis van Gaal can't collect wins on the bounce and it's little wonder the chorus of pundits crow every match could be the Dutchman's last if the Red Devils fail to collect three points.
Manchester United failed to build on their win over Swansea City to start 2016, settling for a 3-3 draw at Newcastle United on Tuesday when Paul Dummett's 90th-minute strike deflected off Chris Smalling and into the upper corner. That was the capper of a brutal day for the defender, who was booked for his wrestling-style takedown of Aleksandr Mitrovic in the 66th minute leading to a penalty conversion to get Newcastle even for the first time after falling behind 2-0.
"We threw it away," van Gaal groused to the team's official website. "You have to finish the game much earlier. The referee gave a penalty and I think it was a duel ... but the referee did not lose our game. We lost it by ourselves."
The result left United with one win in their last eight league matches (1-4-3) and failing to produce a victory at Anfield would mark the first time in the Premier League era they would have one win through any nine-match span.
On the bright side, Wayne Rooney's two goals gave him four in his last three matches across all competitions. With 175 top-flight goals for the Red Devils, his next one will put him ahead of Thierry Henry for the most in the Premier League with a single club.
The Merseyside native has just one goal in 11 lifetime matches at The Kop, a United match-winner back in 2005.
If Manchester United are the aforementioned rollercoaster, then Liverpool are the tilt-a-whirl that can create madness every time the ride starts. Jurgen Klopp has been at Anfield barely four months, and Reds supporters already have been through the wringer: pulsating road wins over Chelsea and Manchester City, turgid draws in Europa League, confounding and comprehensive losses at Newcastle, Watford and West Ham. But most recently was an electrifying 3-3 home draw versus joint-leaders Arsenal while the list of limping wounded due to hamstring injuries ebbs and flows on a weekly basis.
Liverpool secured their point Wednesday against the Gunners courtesy a 90th-minute volley into the lower left corner from Joe Allen, who met Christian Benteke's header sent across the box. The last-gasp equaliser sent the always-combustible Klopp racing around his box and sideline, beating his chest in delight as the snowflakes swirled around Anfield.
It was a deserved draw considering Roberto Firmino twice gave Liverpool a lead in the first 19 minutes, his second a beautiful curling shot into the upper right corner from outside the box. The brace marked his first two goals with the Reds, and he is eager to deliver more.
"I hope I can play like that against all teams, not only the big teams," he told Liverpoolfc.com. "There was extra motivation against Arsenal. I'm sad that we couldn't win the game but I'm happy that I could help the team by scoring two goals, and at least we got a draw in the end.
"Manchester United are a big team and I know how big this derby is here. We have to be 100 percent focused. If we do as well as we did up front (against Arsenal), we have a good chance to win Sunday."
Klopp's coaching box gesticulations and mannerisms again drew attention Wednesday, with Arsenal counterpart Arsene Wenger asking the German to calm down after he accosted the fourth official. While both cheerfully downplayed the discussion, unlike his tete-a-tete with Sunderland's Sam Allardyce, Klopp likely won't have a foil to converse with Sunday given van Gaal rarely strays from the bench area and jots down notes of observation.
Dejan Lovren is likely out for this match, leaving Mamadou Sakho and Kolo Toure likely to partner in central defence once more. Steven Caulker, who was signed on loan from Queens Park Rangers, is expected to bolster backline depth this time after Klopp deployed him as an emergency striker versus Arsenal.
United ran out 3-1 winners at Old Trafford in the reverse fixture as teenager Anthony Martial's 86th-minute goal secured three points in his Premier League debut. Daley Blind and Ander Herrera scored earlier in the second half before Christian Benteke pulled one back for Liverpool with a stunning overhead volley six minutes from time.
Manchester United have won seven of the last nine between the teams in all competitions and are seeking their second straight double over Liverpool.