Your opponents can just kill Rubinia to get their creature back and, as a creature itself, it's more vulnerable than enchantment-based Mind Control effects
Meanwhile, Mystic Sanctuary is actually very, very good in our deck
(Choose any number of permanents and/or players, then give each another counter of each kind already there.) Illustrated by Nicholas Gregory Standard Not Legal Alchemy Not Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
Donquixote Doflamingo (Alternate Art) (PRB02-011) Premium Booster -The Best- Vol
Exiling any nonland permanent is a brilliant start, offering universal removal to get yourself out of the tight spot youre likely in after committing turns to the ramp and color fixing necessary to cast the card
While a fair card by cube standards in terms of power level it is a uniquely positioned card that winds up seeing more play than any of the other creatures that generate cards when they attack like the classic Ophidians and Shadowmages.Viper is a win more card like those others but Viper is substantially better when behind and actually does relevant work