Playing as Bard, how necessary are additional skills?

[SeraviEdalborez]

You have the names mixed up. Tumult is "stomps". Geocrush is the jumping break-the-platform attack. If you use BFB immediately after Tumult ends, he will generally always not use it again until BfB has worn off or is about to.

tl;dr, comes with experience.

[Tharian]

I have only really fought Titan (Hard) twice, and haven't fought Titan (Story) in quite a while. As for Titan (Extreme) I still haven't unlocked it yet. So you will excuse me if I haven't yet mastered what the names of all of his attacks happen to be. I still say Blood for Blood is a bit risky. That said, I will not deny that the extra 10% damage is a nice addition to have on occasion. That said, I am not entirely sold on wasting my time trying to get Mantra. I think I would rather use Feint in that Cross-Class Slot all told.

[SeraviEdalborez]

Then don't give advice on a fight you're not experienced at.

Feint is literally worse than picking nothing as a crossclass. Wasting time on using it, wasting time reapplying it with diminishing returns for the few bosses that do not resist it. TP sink. Weaker than everything.

[RinchanNau]

Can't imagine not using bfb, ir, invigorate, and sw. As for my last cross class, I use featherfoot. Seems more useful than mantra since we don't get the good version than MNK has.

[Katchii]

Feint is useless, not because the skill itself is useless it's because you'll never use it when compared to everything else you have along with the diminishing returns it has. It's a DPS loss, and a waste of TP compared to your other skills.

I always use B4B with Relentless Strikes and Hawk's Eye for really nice burst, and follow that up with Raging Strikes + Internal Release, the cooldowns just line up well that way.

Invigorate is a must have at end game, mainly due to the lengthy fights, and for Expert Dungeons, the AoE that you'll be doing and likely using Ballad for the healers mana or Requiem for the BLM damage rather than Paeon for your own TP.

[Alcyon1]

While the DPS boost from Blood for Blood is indeed really nice, the problem is that it gives you just a 10% boost to damage on Bard, while at the same time increasing the damage you yourself take (incoming damage) by 25%. This trade off is problematic in fights such as Titan (Hard) and (Extreme) where you are constantly bombarded with AoE's, many of which are unavoidable. So while it is useful to have an increase in damage, it is not essential.

Just LOL.
As people pointed it, don't use B4B with the wrong timing. For Titan EX, since everybody is packed, getting hit by WoL means death, with or without BFB. For the Tumults, the WHM will (pre-)cast some AOE heal, with or without BFB doesn't really change anything. The only moment when BFB is dangerous is when Titan jumps, but you can remove the buff by clicking on it.
The only moment when BFB was dangerous was against Twintania, pre-2.2, when your were using the strat "Fireball = tank+pet+target".

BFB IS essential, unless you don't want to kill the high-end bosses without being carried. Invigorate and Internal Release are even more essential.

I'm using Invigorate, BFB, IR, Second Wind and Featherfoot (the last one is virtually useless).

[PArcher]

Anyone who says BFB is bad due to the 25% damage increase is not someone to take advice from.

There are very few, if any, CDs that can be used whenever without penalty (even if that penalty is just you don't have it until the cool-down ends...which can be bad). You have to know when its best to use each one in every fight.