It has a use at the beginning of battle if you can't reach the other side... use focus and wait for them to come to you. Although if you got Growth or Giant Form it is completely useless.

yea, I guess its only meant as a buff to really expensive spells.

(like, a spell that costs more than 4x the mana cost of focus)

Yeah I agree, it has it's uses on large maps or long battles.

either no casting time ... or no mana cost.

Consider that if you have focus, you're (at the very least) a mid level fire mage with two long range damage spells you could start casting instead from turn one. You don't often find yourself thinking - well, the enemies aren't in range yet, so I may as well blow two turns buffing myself up. That's a melee thought. If you have focus, you're ready to go and start fireballing people from turn one, you don't have those two turns to spare. No mana cost or no cast time (i.e. takes only 1 turn) might improve the skill, but.. it's still antithetical to a mage who should be frying enemies from the first turn in a tactical battle that will generally end by turn 5.

Focus would be a better skill if it made your next spell (only) have no cast time and hit 50% harder. Now instead of 2 turns for a regular fireball, you spend 3 turns (2 for focus, 1 for the no-cast-time fireball) to get a +50% fireball. Same damage-per-cast-time, but better mana efficiency and a couple minor side bonuses. If the focus cast gets interrupted, you only lose focus' marginal mana cost, not the full fireball mana cost. Also if you cast fireball normally, you're committing to fireball at the end of that cast time; if you cast focus instead, you can choose any spell on the spot to use your focus on.

I use it if I am in a fight that's going to take maybe 5 rounds, so yes, I use it a fair bit.

I don't use it in its current form. For a mage, there are plenty of passive damage boosters that make +25% irrelevant; for a melee champion, trading two action for +25% future damage makes little sense when you could be spending those actions dealing 100% of direct damage.

Previous version of this spell -- no casting time, double damage for one action -- was more interesting. I used it often to power-up individual spells, and it gave a good reason to upgrade fire magic for melee champions (direct damage spells are worthless without path of the mage, but focus is still applicable to melee attacks).

Not sure why focus was nerfed; probably because it allowed double-damage flame darts to be spammed continuously, effectively voiding their cooldown. Increasing cooldowns and/or nerfing the effect a bit might have solved that while keeping the spell interesting.

Generally, I am a fan of spells that require a timely tactical decision to be made: curse and old focus are great examples. I find spells which are cast once at the beginning of battle boring; they are either no-brainers (blind) or useless (new focus), and result in both sides spending initial turns buffing / debuffing rather than engaging in combat. Such spells should become strategic enchantments with an upkeep or be delegated to item stat boosts, while the tactical battlefield is reserved to time-sensitive actions. Some examples:

• Haste (strategic): initiative +2(+1/air), upkeep 1/season
• Haste (tactical): target moves immediately (single-unit version of battle cry)
• Gust: target misses next action (single-unit version of titan's breath)
• Slow: initiative -4(-2/water) for three actions
• Focus (fire3): +50% damage for next action, no cast time
• Meditate (water3): -50% mana cost for next action, no cast time, no mana cost
• Concentration (air3): +50% spell mastery and accuracy for next action, no cast time
• Blind/shrink/grow/giant form/arcane vale: time-limited, akin to curse and diamond skin