Trinity doesn’t imbue any of your equipment, you can use trinity to simulate the effects of equipment you’ve already encountered in your run. Body form let’s you temporary gain an enchant or glyph, mind form gives you a use of a wand or thrown weapon, spirit form gives you use of a ring or artifact. If you were choosing darts then you were probably using Mind Form, which means you can cast the mind form spell to trigger the effect of whichever tipped dart you selected, as if you were throwing a real tipped dart of that type. Obviously it’s not that useful for simulating items you already have, but the power is in the flexibility. Maybe you’re all out of a particular type of seed but would like to be able to trigger that tipped dart’s effect anyway in a pinch, for example.