Yes, this sounds counter-intuitive. Who would want to buy things that makes their character less powerful? The answer is end-game people who like to show off. These trinkets will show up graphically on a character's hands.

Training Weights:
Trinkets that reduce your movement and attack speed. In return, they give your shield X% more health in both Clockworks and Lockdown.
3* version: MSD+ASD low
4* version: MSD+ASD med
5* version: MSD+ASD high
(buffs scale slightly with star level)

Appearance: Metal bracelets appear around the wrist region. They glow periodically, like halos. Available in different colors.

Snipefeather Mittens
Trinkets that reduce your sword damage. In return, hearts/pills heal x% as much as they normally do in Clockworks and in Lockdown. You also heal at a faster rate on heart pads.
3* version: SDD low
4* version: SDD med
5* version: SDD high
(buffs scale slightly with star level)

Appearance: Feathery mittens (much smaller than power mitt) cover the hands. During sword animation, some feathers fly off. Available in different colors.

Hyper Ticker
Trinkets that reduce your health but also reduce all cooldown times (pet, dash, etc.) by X% in Clockworks. In Lockdown, they let you capture points faster (reduce total capture time by X%).
3* version: -3 bars hp
4* version: -4 bars hp
5* version: -5 bars hp
(buffs scale slightly with star level)

Appearance: A rather unwieldy looking wrist watch around the wrist region that sputters occasionally from time to time. Available in Gremlin or Spiral style.

The Ring
Very rare trinket (perhaps sold only on very special events). You always take damage as if you have no defense (ie. "recon skulled"), you have the maximum susceptibility to all statuses (ie. least resistance). Finally, all your attacks deal fixed damage, regardless of target resist or weapon used.
1 damage in T1
11 damage in T2
111 damage in T3
^Note that this may not be a debuff if you know how to use it wisely!

Appearance: A shiny ring that appears on the dominant hand. Every time you log in, there's a chance the ring will equip itself as one of your trinkets. Any existing trinket will be unequipped. This all happens without your knowledge, and can occur even if you don't have trinket slots unlocked! If you haven't entered chat for a long time, having the ring equipped will cause you to spontaneously utter "My Preciousss...".