With the new command you'd simply use:
[10:16] <@Ehlanna> !weight this(10) that(90)
[10:16] <@Desdaemona> Chose option: 'that' for Ehlanna from the 2 weighted options
Like the !choice command you can use multi-word options
[10:18] <@Ehlanna> !weight "this one(10)" "that one(90)" another(100)
[10:18] <@Desdaemona> Chose option: 'another' for Ehlanna from the 3 weighted options
Limits are: the weight must be in brackets at the the end of the associated option and be a whole number between 1 and 100 (and inside any quotes used for that option).
The total of the weights can be anything as they are treated as a relative amount so !weight this(1) that(2) other(3) being the same as !weight this(10) that(20) other(30), which makes "that" twice as likely as "this" and "other" 50% likely to be picked: 30 is half of the total weights (10 + 20 + 30).
!whoice is a valid synonym for the command.