These abilities are probably underpowered, especially if they require spending a turn to activate them. (However, like others have alluded to, the pace and flow of combat are big factors in evaluating the balance of skills like this, and we don't have that part of the story.) One other thing you need to clarify is whether the "25% of his HP" means 25% of his
current HP (meaning it would be trivial as his HP gets low) or 25% of his
max HP. I am going to assume this is 25% of Max HP in my evaluation here.
Looking at True Grit, you could frame it as a tradeoff between the damage that the character
would take if they didn't have True Grit activated, versus the damage (health sacrifice) that the character takes under its effect. In general, I wouldn't expect a Tank to take 25% of their health in damage each turn of a normal battle. Against bosses... maybe so, especially if they are Taunting (meaning that you don't need to reduce the expected incoming damage based on the chance of not being hit each turn). So this skill might find its niche in boss fights, but take note of my "turns" concern below.
Looking at Bloodbath., it is almost certainly a bad skill to use. This buff makes your Tank (probably not a super-high DPSer in the first place) 50% more effective on offense (actually a little less than 50%, since he probably has a nonzero Crit Chance before the buff, but to be generous let's say 50%), while costing him 25% of his Max HP per turn. The "neutral" point for a buff like this could be found by imagining your party in a combat with a copy of itself: If the +50% offense allowed this one character to take down an
extra 25% of a rival character's HP bar, the buff is a break-even (on its own; see my "turns" concern below as well). That means that the Tank should (without the buff) be able to two-shot a character from your party! Probably not. Since your Tank is dealing less damage than that, it means that the offensive buff is not worth the HP loss that it entails.
Even more important than the balance of the buff itself is the fact that, unless these are toggles/instant cast skills, you are also spending a turn to activate them! So in addition to health, the tank is also sacrificing an action (which he could use to deal damage, use an item, etc.). This cost is hard to evaluate for True Grit since invincibility is pure utility, but if you're looking at the number of turns that the Tank can survive and be effective with vs. without this buff, the "cost" of a turn to apply the buff should reduce the number of turns in the "with the buff" scenario by one. For Bloodbath, however, the cost is much clearer: you've lost an entire turn of offense! The tank will deal as much damage in three turns
without the buff as he will do by spending a turn applying the buff, then attacking twice at 100% Crit. He will also have lost half his Max HP already from the buff's effects, if he uses it. In this light, you can see how using Bloodbath appears extremely disadvantageous in most scenarios.
The final thing to address on these skills might be how to end them. Since the "buffs" have a major malus effect to them, the player might want to cancel out these buffs at some point. Does your game offer a way to do it? Does it cost a turn to do so? Do the buffs naturally wear off over time? Do they end if the tank reaches a certain (low) HP threshold? Or is the design supposed to create a dynamic where the tank is now on a turn timer, and is going to die unless you can finish the enemies off first?
As far as what I might do to balance out these buffs:
- Either reduce the HP loss per turn (maybe 15%, although again, it depends heavily on battle flow), or make it a loss of 25% of current HP per turn
- Give Bloodbath an ATK buff as well as the 100% Crit. The appropriate amount depends on your class balance - ideally, when factoring in the 100% Crit, you'd want him to be hitting slightly harder than an unbuffed DPSer while under its effects
- Consider making Bloodbath an Instant Cast skill
- Consider making True Grit something that can only be used once per battle. If you do this, you could probably also eliminate the HP loss per turn and no-heal debuff (assuming that True Grit will end after a certain number of turns)