Guide of Souls

You don't choose a target for Guide of Souls's last ability at the time it triggers. Rather, a second "reflexive" ability triggers when you pay energy energy energy this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.

energy is the energy symbol. It represents one energy counter.

Some triggered abilities that state that you "may pay" a certain amount of energy describe an effect that happens "If you do." In that case, no player may take actions to try to stop the ability's effect after you make your choice. If the payment is followed by the phrase "When you do," then you'll choose any targets for that reflexive triggered ability and put it on the stack before players can take actions.