I don't cube the Sabertooth but maybe I should
For example, if you attack with a 5/5 creature with trample and it's blocked by a 2/2 creature, you can assign 2 damage to the blocker and 3 damage to the defending player
It is usually only played when it can be cast off the back of a Channel or you are splashing for other ways to cheat it in
The result is that if you can land both on the field you can fire the ballista ad nauseam, stacking counters on it and taking them off to inflict infinite damage and gain infinite life
You can, at instant speed, do three things, but the Mana Leak won't counter anything, so what this does instead is bounce up to three things which can set back folks deeply, bounce two and replace itself, draw three cards when the bounce isn't needed, or bounce once and draw twice