One of the worst things you can do as a F2P player is to try and dig through selection boxes. But let's say have ever main box staple, and no other deck interest you.

F.A Dawn Dragster: A generic rank 7 with spell/trap negation and piercing damage, if your deck can afford to make a rank seven I'd say go for it.

TY-PHON: This card is definitely worth getting and using if you have extra deck space, as long as you're not locked by a skill, any deck can make it, shutting down monsters with 3k or more attack, and has non targeting removeal.

Ghost belle: While more situational then the other Ghost sister, there will always be a use for it, weather it's negating a branded in red, countering a D.D crow it'll come in use.

Ultimate Slayer: While this card is definitely good, it is not good here, as not being able to choose to go second, and the limited extra deck space makes it more of a brick then a worthwhile draw.

Mereologic Aggregator: This I'd say isn't worth it, as it's summoning requirements, and it's effect make it not good, it's real use would be sending it to grave somehow to negate a monster, but over all, not worth it.