So talking to my friend, and he says he is going to build a deck around door of destinies and reassembling skeleton. Apparently, when you play that card from the graveyard, it counts as a spell and puts a counter on doors. Is that true?
{Reassembling Skeleton}
{Door of Destinies}
I'm afraid this does not work. Reassembling Skeleton uses an activated ability, not a spell, in order to place himself back onto the battlefield from the graveyard. Note the COST : EFFECT format of the ability that you will see on all activated abilities.
In order to activate the Door's ability to add counters, a spell must be cast. A spell is cast by playing it from your hand and adding it to the stack (as spells typically are), or by some special effect allowing it to be cast from elsewhere. It is noteworthy that these effects will all specifically say "[you may] play/cast [the spell]." (Ex: the cascade keyword on {Bloodbraid Elf})
He's going to be bummed, but thank you. It's best he knows now before sinking money into it.
{Gravecrawler} can work