MArcomage

with the changes for Christmas, this card ("Reinforcement") and "Revolt" give cards with keywords !?

Yes. I advise reading the change log for more details.

i found the card kinda usefull but why is it so underused?i think it should give higher chances to draw uncommon and rare cards then just by drawing does it function that way?

Yes, every summoning/replacing card bypasses the game's draw chances mechanism and has equal chances of drawing cards (1/3 for common, uncommon, rare).

EDIT
The 1/3 is only a rough estimate, because it also depends on the card pool that the summoning card targets at.