Courtesy of Wizards of the Coast (WotC) and EDH Turn, check out this legendary Hydra Horror from Zendikar Rising — Grakmaw, Skyclave Ravager!
For three mana, Grakmaw’s enter the battlefield trigger bumps it up to a 3/3, but it’s unlikely to keep those stats for long. As an added bonus, having cards like Hardened Scales or Conclave Mentor on the battlefield when casting Grakmaw will give you a big threat right away.
Whenever another creature you control dies, if it had a +1/+1 counter on it, put a +1/+1 counter on Grakmaw.
For Constructed purposes, Grakmaw appears to fit best in a sacrifice or aggressive shell packed with small creatures that also have +1/+1 counters. As those creatures die, Grakmaw can get big really quick.
When Grakmaw dies, create an X/X black and green Hydra creature token where X is the number of +1/+1 counters on Grakmaw.
This final ability acts as a great insurance policy against most spot removal and sweeper spells, allowing you to continue pressuring your opponent.
Since Grawmaw is also a legendary creature, it makes it a prime target to build around in Commander, where there is no shortage of +1/+1 counter synergies. Plus, with Commander’s latest change to how death triggers work, Grakmaw will spawn the token before returning to the Command Zone so you can do it all over again.