Cover?

[Maelwys]

Cover's only white damage though, right?

I guess 2 paladins against titan (yeah, unlikely to happen, since premade wont have 2 tanks, and df titan likely wont have the cooperativeness) can't have the MT pld sentinel through the first buster, and then 2nd pld covers up MT pld on landslide and then sentinel himself for the next buster.

Not sure what you mean by "white" damage...? Cover's only Physical damage, not magic. But it applies to Weaponskills and Autoattacks alike.
Titan's "Mountain Busters" might count - not sure if they're Magical or Physical.

If they're physical, you could have the OT use Bulwark --> Cover --> Sentinel on the MT in that order (as long as they leave a second or two after Cover before activating Sentinel - It's 10 sec duration and Cover is 12, so that works out OK!) but you'd need to stand very close for Cover to work without getting hit by MB yourself (you don't want TWO doses of damage!!) and let the healers know what you're doing, since they're likely to be focussing on the MT.

Realistically though, it's usually not the Mountain Buster that kills the MT since they're usually topped up (unless they eat a bomb and aren't cured in time) but the fast followup hits. Assuming that you have an OT (Yeah, I think that only happens in Duty Finder fights or FC carries!) an OT could just Provoke off the MT immediately off the MT whenever they see Mountain Buster animate. As long as the OT stays at about 95 degrees to the MT (well to the side and SLIGHTLY back) they shouldn't get hit by MB, but would get whomped by any follow up hits - that'd give the MT a chance to get topped up again and reclaim hate. You'd still need to be careful of the stomp/plumes that happen after MB, but a Tank should be able to weather them OK.

(I still think you'd be better off as an OT PLD just DPSing and spamming Flash though - Titan can be blinded for pretty much every Mountain Buster and stomp (just be careful due to DR) and the MT will be busy spamming their +Enmity combo trying to keep healer hate after the Heart phase)