When purchasing high-value cards over hundreds of dollars, always buy Graded (PSA/BGS) or from trusted sellers
For example, Captain Storm, Cosmium Raider from the Lost Caverns of Ixalan release has an ability that says "Whenever an artifact enters the battlefield under your control, put a +1/+1 counter on target Pirate you control." If an artifact creature enters the battlefield under your control, that ability won't trigger
For this to be good, your creature already has to be great -- and in Limited that's not very likely
Artwork : Alternate and full-art cards are more desirable due to their visual appeal
Parallel artwork and visual variants should not be added to that figure unless the official checklist counts them as separate types
One thing that doesnt work is Frenetic Sliver as the ability states the creature must be in play for the coin flip to happen, so while you can activate it as many times as you want you can only resolve it until the creature dies