Success means they are unaffected that round. Failure means they suffer 1d4 ability damage in the relevant ability score, and you gain points in the same ability equal to 1 per creature damaged in this way. You retain these points for 10 rounds after the spell ends. If the lantern is destroyed, the spell ends immediately, and you lose all leeched ability score points.
Deep Magic. � 2014 Open Design LLC. Authors: Wolfgang Baur, Tom Benton, Creighton Broadhurst, Jason Bulmahn, Ross Byers, Charles Lee Carrier, Tim Connors, Adam Daigle, Jonathan Drain, Mike Franke, Ed Greenwood, Frank Gori, Jim Groves, Amanda Hamon Kunz, Sam Harris, Brandon Hodge, Phillip Larwood, Jeff Lee, John Ling, Jr., Chris Lozaga, Ben McFarland, Nicholas Milasich, Carlos Ovalle, Richard Pett, Marc Radle, Stephen Radney-MacFarland, Wade Rockett, Stephen Rowe, Adam Roy, Amber E. Scott, Neil Spicer, Owen K.C. Stephens, Joshua Stevens, Christina Stiles, Matt Stinson, Stefen Styrsky, Dan Voyce, and Mike Welham.