Quest with Life Splinter | Splinterlands

The life splinter brings smile and happiness on my face for the first time otherwise I don't like to play with Life. :D I grabbed a nice reward at the end of completing quest. Got one gold foil card from Death Monster. I never used this card since my joining. I have to figure out what's this all about and when to use in battles.

If anyone of you know when to use UNDEAD card, lemme know.