The card also hasn't been tested at all, so I make no promises about it. The PCs in my campaign short-circuited the encounter before the henchmen could even show up. They dropped the villain to within 2 wounds of a KO before he could act (or call for help), and then shot him again after he surrendered.
My plan had been to use the "Overboard!" card from the Dreadfleet Captains POD expansion as the "new terrain card" mentioned on the triple-success line, but you might choose a less daunting card if your water isn't quite so deep and fast.
MINOR SPOILER ALERT: The above card is very loosely based off an encounter from The Enemy Within, and to a lesser extent the Grapple card from the core set. I scaled it back considerably from the effects of the opposed Athletics rolls on page 132 of TEW because the original tests were a bit over the top. In the adventure, the NPCs only needed a single success to automatically knock a PC out of the fight. This meant a simple Ruffian NPC with 1 Expertise had a 30% chance of effectively one-shotting a min-maxed melee-oriented PC and as high as an 80% chance of doing the same to the party's wizard or other low-strength character. I know the game is pretty deadly, but those numbers seemed un-fun. My version cuts those numbers down to 7% and 20%. (GM's who feel I'm going too easy on the PCs could change the triple-success line to a double-success line to set the numbers at a more threatening 16% and 63%.)