Ardent Censer on Support Trundle is Actually Really Strong!
I am trolling! Get it? Because it is Trundle... no? Okay, fine then, moving on!
Clearly it is for that 1% more max health damage on your ultimate because of the ability power. I am being sarcastic by the way, that is not why you get it for support Trundle.
So if you take the mastery where your movement impairing effects applies the healing mark then you have a way to "heal" allies when they attack targets slowed by your pillar (and bite slows briefly too). So then you can give everyone Ardent Censer buff and yourself the buff as well, which Trundle loves some attack speed and on-hit damage because outside of his ultimate, he can only deal damage from basic attacks. And then the other stats are good for Trundle with mana regen, movement speed and CDR. This would be the only non-tank item to take, the other items should be things like Knight's Vow and Zeke's Something (it is pretty good since your ultimate steals stats and the item gives a bunch of damage, which means the active effect is even stronger since it is a lot more effective damage).
Anyways, for support Trundle it is really strong, keeping in mind you HAVE to take the one support mastery that marks movement impaired enemies otherwise you are legit trolling since it is the most useless item on him otherwise, but super strong if you can actually get the passive to activate.
For support, I like Glacial Augment for the added slow, especially since Trundle is melee (duh) and has the empowered slow with 45% CDR for more pillars and ultimates and all that and then Resolve tree secondary for the mark to healing mastery and resistance mastery for more tankiness since you are a tank support.