It emphasizes aggression, removal, and sacrifice mechanics
If enough -1/-1 counters are put on a creature you control at the same time to make its toughness 0 or less (or the damage marked on it to be lethal), the number of +1/+1 counters on it before it got any -1/-1 counters will be used to determine how many Mutagen tokens you get
In all seriousness, though, a panic button available to any deck is something to be wary of, and its appreciated that designers were mindful to limit the potential for annoying scenarios by making this legendary and having it exile itself on activation
The odds of discarding your hand if you have a full grip is only 35%, which isnt awful, but think about the other 65% of the time where you get to draw two cards or return something to your hand
Incapsula incident ID: 1816000830633149369-525345466164450551