A neat thing about the cards in modded Rounds is that they can be more or less valuable depending on whether you're playing 1v1 or 3-player free-for-all.
Some cards if taken in 3-player free-for-all are a death sentence. For example, the "one-hit wonder" card (all damage dealt and taken is lethal) and the cursor gun card (shoot 4 bullet in a cross pattern from wherever your cursor is) invite death. I've played a lot of 3-player free-for-all with my friends. If you take one of these cards, the other two players must team up every round or else get destroyed by this deadly card while fighting each other. [Blah blah game theory equilibria Schelling point blah.] It's their common interest now to team up against you, so they probably will. That makes the card much less valuable, because the huge advantage is offset by always having to fight two players at round start instead of one.
Conversely, in 1v1 — which is the only vanilla mode — there's no reason not to take them. Unless your opponent has some card that benefits from you taking this powerful card, they get nada. There's nobody for them to coordinate with. Suddenly that card is worth a lot more.
In theory, this Rounds mod supports team deathmatch. I haven't played it because we never have more than three players. Probably the dynamics change interestingly there, too.