Valnamor is a legendary water summoner which can make your water monster powerful. He makes all friendly monsters faster, gives 1+ health to all monsters and 1+ magic attack to all magic monsters. Though this card is expensive you can use Valnamor to win tournaments or move higher leagues to get more reward cards. The worst game mode to use this card is silenced summoners because in this game mode all summoners don't have any advantage to use at matches. I would use this card at high mana capped matches because sometimes you don't find place to use cards.
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From @spritoffreedom