Most of the time I am building a deck because of a card that I like, or a combo I didn't see until I saw two cards interact. An example of the latter is that while playing a game on arena, I noticed that with mythweaver poq in play that the lands that could be played as spells, specifically permanents, would have the second copy of the land actually enter as the permanent, and there is no option to put it into play as a land. I never would have thought that was how it worked but quickly built a deck focused on this and it is fun and affective, seemingly catching some opponents off guard that may also have not realized that this was how it would work. It really seems like a cheat as it can mean getting a free spell that should cost 5 or more and still having all my mana available. I then took into consideration that I could only have one poq in play and only 4 in the deck, and with it being the card that makes the deck special, so I then focused on cards that would ensure I got a copy early and/often, like tutor like effects, or since it's Green, a few cards that let me look at x cards and put a permanent in my hand. Then I made sure I had several cards capable of keeping it in play, by bestowing hexproof and/or indestructible or even exiling it temporarily to even avoid being forced to sacrifice it, and even a few cards that could retrieve it from the graveyard if I failed to properly protect it. I looked at all the other land/spell cards on the colors I had ended up picking, and even though they don't work with poq, if they aren't permanents, in fact I don't even get a second copy of the land, there were still a few that felt as though they fit in with the overall theme, and I have been enjoying playing it, and may make another version with different colors to see how well it works.
Most of the time I am building a deck because of a card that I like, or a combo I didn't see until I saw two cards interact. An example of the latter is that while playing a game on arena, I noticed that with mythweaver poq in play that the lands that could be played as spells, specifically permanents, would have the second copy of the land actually enter as the permanent, and there is no option to put it into play as a land. I never would have thought that was how it worked but quickly built a deck focused on this and it is fun and affective, seemingly catching some opponents off guard that may also have not realized that this was how it would work. It really seems like a cheat as it can mean getting a free spell that should cost 5 or more and still having all my mana available. I then took into consideration that I could only have one poq in play and only 4 in the deck, and with it being the card that makes the deck special, so I then focused on cards that would ensure I got a copy early and/often, like tutor like effects, or since it's Green, a few cards that let me look at x cards and put a permanent in my hand. Then I made sure I had several cards capable of keeping it in play, by bestowing hexproof and/or indestructible or even exiling it temporarily to even avoid being forced to sacrifice it, and even a few cards that could retrieve it from the graveyard if I failed to properly protect it. I looked at all the other land/spell cards on the colors I had ended up picking, and even though they don't work with poq, if they aren't permanents, in fact I don't even get a second copy of the land, there were still a few that felt as though they fit in with the overall theme, and I have been enjoying playing it, and may make another version with different colors to see how well it works.
Fun/intersting interactions are usually the catalyst of decks for me as well lol. I actually didn't know about that interaction ^^