Loom: Unless I got my only defective Turbo game when I bought it new, the game was glitchy and buggy throughout. Garbled graphics at times, crashing, saves that don't work, etc.
If we're counting design flaws/imperfections, then:
Night Creatures: gameplay essentially broken and you can be juggled infinitely by enemies.
Cosmic Fantasy 2: status ailments don't exist(?)
Dragon's Curse: sneaking into Tiger Man's dungeon and defeating the boss gives you all of the game's transformations.
Shape Shifter: Holding down jump while transforming makes your character jump once they transformation is complete, even in mid-air. Allows you to fly through the game and potentially skip 90% of it, once you get the Shadowcat form.
Non-Turbo bugs:
Monster Maker: if you don't complete a particular dungeon towards the end of the game in one go, the game can never be completed. Wasting dozens of hours of playtime.
Hi Leg Fantasy: the game gave to memory space warnings, saving for the first time simply wiped out all of my game saves, including one for Cosmic Fantasy 3 approximately 2/3 through the game.