Unupped seems op statwise, upped is a very marginal improvement if at all, so can stay the same.
Is the active ability truly random or will it prioritize unmarked cards? Since it affects cards in your hand that are leftover (and its possible to empty it relatively quickly), weapons are a pretty likely target, plus you can reasonably run more than 6 of them now. Its a bit daft though that the replacing rather than the to be replaced weapon is more likely to be marked. I do think the effect is strong enough to warrant some extra cost compared to a vanilla creature, but despite the incredible mana efficiency a rush based on longbows and swords will probably take too long to make the marking of weapons relevant enough to outperform an ordinary rush, a mono with lot of OE however would be simple to build yet incredible powerful (i find myself running 3 to 4 OE without any flying weapon in stalls, so that has serious potential). Of course its vulnerability to CC and summoning sickness, as well as synergy with other marking cards have to be taken into account.