Monster skills

Someone please explain to me what does each skills do in simple English, I have hard time understand and always screw up.

1: Bloodthirst - This skill hits 1 enemy, it deals more damage for each kill made by the ‘USER’ in this battle.  User meaning my own monster or anyone while the monster is summoned?

2: BloodCrave: This skill hits 1 ememy, it deals more damage for each kill made by the ‘USER’ in this battle.  but some of it’s reflected back on the user.

3 - How do I know which skills does how much damage? What is the skill ranks.

Super, Mega, Giga, lux Ultra etc.

  1. Also, do you ever use “survivor, 400 sec timebomb, last stand” skills? Either my monsters do tons of damage that they never need to use this skills or they die too fast that they can’t use skills I listed above.

The longer the skill takes, the stronger it is (for elemental spells)

Like ultra takes 250 seconds

Bloodthirst and crave; if that monster has killed an enemy already, it does good damage

Those skills like last stand and 400s bomb are niche, but can be used often with good setups and do extreme damage