The total is 26%:

To kill the Dreamers: 1% - Monomon 1% - Lurien 1% - Herrah 1% - Dream Nail

To get to the Dreamers: 1% - Uumuu 1% - Watcher Knights 1% - Vengeful Spirit 2% - Mantis Claw 2% - Crystal Heart (These are the %s a Low% non-TE run has)

To kill Traitor Lord: 1% - Hornet 1 2% - Mothwing Cloak 1% - Hornet 2 2% - King's Brand 2% - Shade Cloak 1% - Traitor Lord

To complete White Palace: 1% - Broken Vessel 2% - Monarch Wings 1% - Dream Wielder 1% - Awoken Dream Nail

Then, lastly, you have Void Heart itself, as 1 more %, adding up to 26%.