Jalmari Helander hasn’t made a feature since 2014’s “Big Game,” then the most expensive Finnish film to date. It was an unabashed, bombastic, good-humored action crowd-pleaser that indeed pleased crowds — at festivals, while mysteriously failing to catch on with general audiences. Presumably his concept was just too “high” for mainstream viewers to swallow: Though they don’t have any problem with Gerard Butler or Will Smith doing similar honors, it seemed too much to accept a 13-year-old Finn boy singlehandedly rescuing the president of the United States from an obstacle course of assassination peril. 

That failure must have hurt; Helander has spent the interim on episodic work. His new “Sisu” is, in many ways, cut from the same cloth as “Big Game” as a splashy popcorn action piece unconcerned with credibility, pushing well-worn ideas to outlandish, and outrageously entertaining, ends. But the writer-director has hedged his bets by moving one key piece in the game to the opposite end of the board. This time, instead of a juvenile protagonist that made viewers wonder whether they were watching a movie for kids or for grown-ups (the answer “both” apparently confused them), we get a crusty coot quite spry enough to take on all foes. Which bad guys might pretty much be termed “the entire Third Reich.” 

The resulting mashup of Liam Neeson-esque “arse-whupping senior” and “Inglourious Basterds” terrain is a one-joke movie that manages to sustain said joke with esprit. Gleefully over-the-top, utilizing explosions and gore to comic effect as expertly as Buster Keaton did pratfalls, it’s a bad-taste, feel-good exercise likely to delight many, even if it’s definitely not for everyone. Sony has already acquired the TIFF-premiering, English-language production’s international rights (outside Nordisk territories), with U.S. distribution still up for grabs. Prospects should surely restore the director’s commercial luster at least to the level of his 2010 debut, macabre Yuletide fantasy favorite “Rare Exports.” 

Opening text explains the title as an untranslatable local term for “a white-knuckled form of courage and unimaginable determination … [manifested] when all hope is lost.” Then map graphics briefly summarize Finland’s battered straits during WWII, when first it had to fend off Soviets trying to re-annex a nation that had declared independence just two decades before, then it found itself overrun by Nazis. By 1944, when this story is set, Hitler’s armies were in retreat, their war all but lost. Yet as they were forced homeward from the battle zones of Lapland by Allied forces, they were determined to “destroy everything in their path.”

It is amid those stark northernmost landscapes that we meet a man who’s “decided to leave the war behind him, for good.” Alone but for his horse and dog, this grizzled prospector (Jorma Tommila) is panning and digging for gold. Indeed, he finds a fat vein, his good fortune resulting in a hefty bag of nuggets. But the war is not done with him yet.

Back on the road with that loot, he encounters a substantial German squad encompassing tank, troops and captives (a half-dozen grim-looking young Finnish women) led by glint-eyed Bruno (Aksel Hennie) and sleazy subordinate Wolf (Jack Doolan). While they’ve laid waste to local residents just because, they seem inclined to spare this old man, who looks half-dead anyhow … until his mineral stash is discovered. 

These pickings should be easy. But the gray-bearded relic turns out to be a startlingly nimble, resourceful and lethal adversary who dispatches Axis personnel like a patio zapper does mosquitoes. They soon realize they’ve stumbled upon one Aatami, reputed to have taken 300-plus Russian soldiers’ lives after the Red Army killed his family. They dubbed him “the Immortal” for his seeming invincibility, which is rapidly proven here to be no myth. Still, despite skyrocketing casualties and official orders to reverse course, greed drives Bruno to continue pursuit.

Proceeding in chaptered episodes (with titles like “Scorched Earth” and “Kill ’Em All”) of about 10 minutes each, “Sisu” resembles nothing so much as a live-action Road Runner cartoon, albeit with considerably more graphic gore. Each offers a set-piece in which Aatami turns preposterous odds to his advantage, whether in a minefield, surviving a hanging or clinging to the outside of an airplane. 

The combination of deadpan tenor — our hero is so laconic, he doesn’t speak a single word until the fadeout — and extreme violence played as precise slapstick manages to avoid monotony through Helander’s dextrous handling. It also renders any quibbles re plausibility moot. Like Tarantino’s “Basterds” without all the yada-yada, this is no history lesson, but purely a fantasy against bona fide evildoers. There are certainly no “good Nazis” here to feel sorry for. And yes, the captive (presumably raped) women do get to exact their own special revenge.

“Sisu’s” outre fun is accentuated by all the first-class design contributors, from Kjell Lagerroos’ very handsome (though never prettified) photography and Juho Virolainen’s razor-sharp editing to the range of viscerally impressive stunt and FX work. Juri Seppa and Tuomas Wainola’s original score incorporates diverse influences while principally evoking the classic lone-gunman cool of Morricone’s spaghetti Western soundtracks. (Among visuals, one notable cineaste in-joke is a climactic homage to “Dr. Strangelove.”) 

Performances are equally on target, archetypal without caricature — the action itself provides cartoonishness enough. Veteran lead actor Tommila’s son Onni returns from starring juvenile turns in both the director’s prior films, though his role here (like all those not previously mentioned) is a relatively minor one.