Ok, I've got some basic methods of doing some of those.
For your bomb enemy, make a battle event with a trigger Monster [your bomb enemy] Turns elapsed [XX] (let's say 5 for this). Then show battle animation of whatever your explosion is, reduce your party's hp by however much you want it to, then reduce your bomb's hp by 100%, and voila, your bomb will be set to explode in 5 turns. It's pretty rigid, but hopefully it's a start.
If you want an attack to do no damage, make sure the damage multiplier for that skill has one letter set to 0% (Maybe you'll want to make your own attribute for the attack getting negated). When your hero uses that fireball//laser/exploding duck, damage will always be 0.
Ok, I'm having trouble getting reflected damage to work out nicely, so maybe you can experiment with it too. So far I've set a battle command to [Hero] uses the [Skill] command, and then changing the hero's hp to however much your laser would have hurt the enemy. Use some battle animations, and it should look pretty believable.
Oh wait, these were in 2K3, but the DB should be pretty much the same. Feel free to change these as much as you need to, too. They're just really basic, experimental events, & there are definitely better ways to make them work.
Heh, that bomb one's really bothersome... I'll start with the 1 hp thing though.
You'll want to make switches for all of your characters, then copy this into every monster group
After you get that down, set up a common event for all your characters individually, make it a parallel process with their switch, and do this:
Now after every battle, your deceased should come back to life </triumph>! The process is a bit tedious though.
Bleh, now for the bomb one... You'll need 1 variable for the turn delay, and 2 switches: one for the skill itself, and one to make sure the skill doesn't keep going off. Start by making your first page add a Bomb! variable every time he takes a turn.
Next page, you'll need a trigger to allow your bomb to use his explosion skill.
Now that he's allowed to use the skill, make it so that he starts the countdown, then can't use the skill again (That was a headache).
Finally, rig him to explode! Oh, if you're wondering why I set the variable to 100, it's because I don't want him randomly exploding in the heat of battle.
There you have it. Only problem is that the bomb will take one more turn before going down, I'll look into that. Oh yeah, I forgot about the bomb skill, my bad. Ok, make yourself a switch skill (I called mine "Warning!" because it shows up no matter what, might as well make it relevant), and have it turn on your first bomb switch.
Ok, this here's the real last step. Make your second switch a condition to use the skill on the Monsters tab
There you have it, way too much work for something that should be pretty simple. Just watch, as soon as I post this I'll find some easy way to do it. Oh well, use it if you want.