Wormwood is usually run as a dart DPS. If you have a Wigfrid on your team consider giving her the Scatter Tooth. It will let her proc Battlecry more often since it hits 3 times and she doesn't care about being close or getting hit unlike Wormwood. His speed perk is not very impactful and you usually wont want to be close enough to use the pollen. Overall don't worry about using the perk, you're playing Wormwood for the weapons. Wormwood can also be run as a healer or mage if you really need it (your playing random characters) since his speed may help you get away from enemies to cast a bit easier. There are much better characters for these roles though so just pick them.
After not being hit for 10s starts blooming, gains an additional stage every 10s. When fully bloomed gain 20% speed boost and drop pollen that reduces enemies damage by 10% for 10s if they are in range (3).
Take all damage items just like any other darts DPS. If you use Molten or Barrage Darts you can just hold F, theres not much Wormwood specific strategy since his perks are pretty weak. If you take Scatter though, make sure you're close enough to hit all 3 darts since doing so is the highest damage per attack of all darts. Final build is Jagged Grand Armor, Nox Helm, and Scatter Tooth (or Molten)
Wormwood does nothing special as a healer or mage, just try not to get hit so you keep your speed. Final build is Silken Grand Armor, Woven Garland, Living Staff