When Murderous Redcap dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Murderous Redcap enters the battlefield, it triggers, dealing damage equal to its power to any target.
Activate Hexavus' second ability by paying ({1} magic symbol) and removing the -1/-1 counter from Murderous Redcap, putting a +1/+1 counter on Hexavus.