Go first for Morale Boost I, because it will help Grohk getting a lot of damage and heal. His ultimate starts getting worse when enemies have bought Cauterize 2-3.
Then, once you die, purchase Cauterize I -> Morale Boost II -> Haven I -> Caut II. You can also purchase Resilience or Chronos, and even Wrecker in situational games.
Try to focus your bounces vs Barik's turrets, Luna, Ying's illusions and Nessa/Vivian deployables. If they're in-game, or to places where there are no shields and your Shock Pulse can bounce.
For the build, the card Astral Traveler is interchangeable (same with the increasing HP, but it brings Grohk a lot of sustain).
Play in point and close to tanks n supports.
Place your totems to gain that healing when you're low or to heal your tanks if support is dead.
You can arrive to get 250k+ dmg if played properly in a 4-3 game!
Your weapon shots reduce the Cooldown of Shock Pulse by 0.5s and Shock Pulse chains 4 additional times.
Heal for 150 for each enemy hit with Shock Pulse.
Increase the Chain range of Shock Pulse by 32%.
Generate 12% of your Ammo for each unique enemy hit by Shock Pulse.
Increase your maximum Health by 150.
Increase your Movement Speed while using Ghost Walk by 10%.
Increase your Ultimate charge rate by 30%.
Your weapon shots reduce the effect of healing on your target by 50% for 1.5s.
Reduce the Damage you take from Direct attacks by 14%.
Reduce the Cooldown of all your abilities by 10%.
Good against illusions and slowy no-shield champs.
Terminus shields avoid Grohk using his bounces. Terminus is a good ban if you're planning to play Grohk.
Bad against shields, too, so if there's 2+ shield champs, buy wrecker.