Welcome to the Swain Zone. While HoB Swain was originally a joke I made with my friends when I accidentally took the wrong runes, I soon discovered that the rune was viable, and began building for it, and getting 20+ kills every other game. Overall, this build is less effective than the normal electrocute build, but it gives you a lot more killstealing potential, and lets you get fed faster.

If you're fed, and you hook a squishy, then you can effectively oneshot them with:
E -> Pull -> Auto -> W -> Gunblade -> Q -> Auto
Hextech Gunblade allows you to auto right away instead of wasting time with your W, as the slow will usually guarantee the W hit anyway. The early auto will allow you to proc Lich bane earlier, which will then allow you to Proc it again earlier.

If you hook multiple people, pull the squishiest one and attack them. Should be obvious.

Early game, you should harass the hell out of your enemy. Your E is incredibly good since it will allow you to get all 3 procs of HoB off, and let you walk away from the trade without taking any damage. You should ensure that the enemy is always on low hp, because before you get your ult, they can almost always win an all-in. Once you get your ult, and the enemy doesn't have a big lead over you, don't poke them as much. You win all-ins with your ult, so bait them into pushing you too hard, then pop your ult and pull them to their death. Your ult gives you a lot of survivability, so while it can be used to dominate 1v1s, it is also very useful for setting up ganks, as your enemy will be fighting you for a long time.

If you're fed late game, you are the Mega Chad. The Win Condition. The Game Changer. You can 1v2, 1v3, maybe even 1v4 or 1v5, and at this point, the enemy knows that. Do not get caught out. Do not start teamfights either, unless your team is in front of you, or you get a good hook on a high damage enemy squishy. You don't want to take the front of the enemies' damage at the start of a fight, unless you're confident that your allies don't need you to hold their hand. Because you'll die early. You want to take damage, though, so once the teamfight starts, walk close to the enemies and embrace them lovingly with your ult.

When to start your ult: Right before taking a lot of damage, or right before getting hit by CC. These situations include running headfirst into the enemy team, so go wild. Make sure that if you're about to die, or a high value enemy is about to escape, to end your ult. While getting its full value is important, killing high damage enemies will do more for the teamfight than your survival will.

Though most of that stuff was just how to behave with normal swain, HoB Swain doesn't behave that different. You just do a bit more damage, and can more easily catch people out. With this build however, you do lots of AoE damage as well as single target, so you can more easily pick out targets in teamfights to auto while you fight.

Good Luck out there, and make sure to ping your longsword/faerie charm at the beginning of games because people find it funny.