Grenade Level Up

[OutlawZ]

Go to Cutthroat isle.
Go inside.
Head to the ramp/hill that runs alongside the river.
Watch out for the Flytraps at the top
and find yourself a spot on the ledge, looking out towards the river .
Below you and to the left, is a large tree with a Stump just waiting to have grenades thrown at him!
And you can practice your aiming.
He will try to attack you, but of course he can't reach you (although some of his attacks may slightly damage if you are too close to the edge).
Take some tonics just in case you need them.