The Trisword is unlocked by defeating the easy dungeon "Terror's End", which requires you to play as a Warlord and defeat Bleaty the Goat. This is by far the hardest of the "easy" missions.
The Trisword itself increases your base attack by +2 every time you drink any potion. As you progress through the game, it becomes possible to prepare a large number of potions and to buy even more from shops. Combined with the potions a gnome or halfling can create, a Trisword can be very powerful indeed.
The Alchemist's Scroll is an elite item, and is unlocked by fully-upgrading Bezar. Complete all the bank and shop-related quests to do this.
Mystera gives you the fireball power to easily take on the Tower of Goo, while Dracul gives you the physical staying power to easily take on Super Meat Man. Your best bet is probably to find one of these deities.