Sesilu, that's from shard of wisdom, a very special case. It's not a bug. It's literally the only card that can target immaterial creatures. As far as dealing with shard of wisdom, I recommend the reflective shield, or the emerald shield. Or sundials. Or the upgraded fire shield. There's plenty of options.
@fenkosmo check the bazaar for cards, farm level 3s, 4s, 5s as well as the arena to get rare cards like weapons, shards, a couple creatures as well as a spell or two. To get nymphs you need to either get lucky at the oracle, or one of the many pvp events. For more information on pvp events, check the forums @ elementscommunity.org/forum/
Hope to see you around sometime.
If anyone is looking to complete the deck wrecking badge, ask in chat and see if anyone responds. If not just click pvp1 and wait about 2 minutes before exiting out and trying pvp1 again, you will get matches.
@GlowingLimes npc ability to use the cards available remains the same regardless of level, the only thing that changes are what cards are available to the npc. All this information is available on the wiki. As it is, the npc is actually really simple and wont come up with any convuled strategy, it will simply play what cards it can and use what creature abilities it can, which can be really annoying when making an Arena deck (shriekers will almost always be burrowed on the next turn as an example). The chances of losing against level 0 is quite low, the npc has to get a really good set of cards consistantly for quite a few turns and you have to either be using the starter deck (not recommended) or just a really bad deck.
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Pickaxes don't have any attack - the steel pick has a lower stamina cost per use (not attack damage), which is why it's better.