What did Monster Hunter Tri change?

It rebooted the series on Nintendo hardware, threw almost the whole bestiary away, and rebuilt it around an ocean.

Monster Hunter Tri was released for the Wii in Japan on August 1, 2009, directed by series creator Kaname Fujioka. It had begun life as a PlayStation 3 title before development costs pushed Capcom to the Wii, and it sold 520,000 copies in its first Japanese week on the way to a perfect 40/40 from Famitsu. North America followed on April 20, 2010, in a bundle with the Classic Controller Pro that taught a new audience the series’ two-stick grammar.

Tri was a deliberate reinvention. Only three boss monsters returned; eighteen new ones debuted, led by the sea wyvern Lagiacrus. The Switch Axe joined the arsenal while several older weapons were cut, bows and gunlances among them, a sacrifice the team later attributed to the cost of the headline feature: full underwater combat, hunts that flowed from beach to seabed without a seam.