If you want to summon in Hidden ATK or Hidden DEF Position an Integration Summon you are not forced to reveal the eroded material card right away, but when you erode it you must set it clearly apart from other cards, and once your monster is revealed or the duel ends you must reveal that the eroded card was the proper material, otherwise you lose the duel instead
It rewards you with powerful abilities whenever a land comes into play, regardless of whether you played it or put it onto the battlefield with a ramp spell
Truth be told, Ohran Frostfang is probably the better card out of the two, but both are really good, together or on their own
Upgrading them is also a ton of fun because it lets you personalize a deck without jumping straight to a wholly unique decklist
My thoughts went to Tegan Jovanka as the Doctor's companion, because it's a cheaper companion that can give a historic creature +1/+1 and indestructible, easing future attacks
Lets check out the most exciting cards