To activate a cohort ability, the Ally with that ability must have been under your control continuously since the beginning of your most recent turn. Informally, it can’t have “summoning sickness.” However, the other Ally you tap can be one that just came under your control. (Note that tapping the second Ally doesn’t use {T} [the tap symbol].)
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.