He nabbed Bird, ending a 68-run opening stand and then trapped Cam Gordon in front second ball, sending Northland from 68 without loss to 68 for two.
Sam Webb, the third leading scorer in the tournament going into the final, arrived at the crease and continued on his good form.
Trigg and Webb reconsolidated and then took the attack to Coastlands, combining for an 81-run stand in the process.
In that time, Trigg passed fifty in a true captain's knock and was on 71 when a good bit of fielding from James Gatenby-Hinton ended his innings.
Northland then lost Alex Gordon for a duck in the same over, leaving them at 151 for four with eight overs to go.
Webb (33) had his stumps knocked over by Timothy Pringle 11 runs later, Northland being on 162 for five with just five overs left.
Max Turner (20) came in and hit a pair of boundaries to help increase the run rate and after Kalani Snooks (5 not out) hit a four to fine leg off the last ball, Northland had reached a very competitive 190 for seven from their allotment.
Northland's initial overs with the ball erred on the expensive side but a double breakthrough soon remedied that, putting Coastlands under pressure.
Brayden Hutchinson-Walters came into the attack and took a pair of crucial wickets in the space of four balls.
His first one had Taylor Bettelhiem (1) reaching at a wider one and nicking it through to Sam Webb at gully, who grabbed it on the second take.
Hutchinson-Walters then trapped Pringle in front for a third ball duck.
Fergus Lellman and Niven Dovey (35) then came together and frustrated the Northland bowlers while putting on a 72-run partnership.
Off-spinner Alex Gordon came into the attack and kept it tight. He was rewarded with the wicket of Dovey which left Coasatlands 92 for 3.
Hunter Dickson (15) joined Lellman and carried on where Dovey left off. They put on 45 before Northland roared back into the game.
Max Turner (4 for 26) came back into the attack and within nine balls had brought Northland right back into the contest.
First he had Lellman caught out for a well-compiled 55 and then bowled out Dickson.
In his next over he nabbed Carson Wills for one, leaving Coastlands on 144 for six.
But Rhys Donaghy (13) and Dempsey (24 not out) got Coastlands within three runs of victory with seven balls to go.
Another twist turned the game again when Nathan Parkes (1 for 18) dismissed Donaghy, leaving the opposition needing three runs from six balls with three wickets in hand.
Turner was given the last over and struck with the first ball, Harry Cooper catching out Braxton Fisher for a golden duck.
He followed that with a dot but Gatenby-Hinton hit two off the third ball, leaving the scores tied.
Northland couldn't quite finish Coastlands off as Gatenby-Hinton hit the winning runs for the two wicket win.