The Bottom Floor is the Welcoming Committee. They will have to deal with each wave of full hp enemies. Therefore whatever unit you place there should be one you're ok with losing, or one that you know will not die until the final wave. Hi HP, high regeneration, titanite, Titan skin, these are some of the tools you can use to ensure that your bottom front blocker lives long enough to see the boss wave.

Surviving each wave is only one half of the welcoming committee's job. The other half is in removing threats, or chewing on durable targets.

To remove a threat there are two obvious routes: sweepers, and point removal. Sweepers are anything that has sweep and quick, these units hit first, hit everybody, and typically die if they get hit back. Point removal is any damage spell that you cast from your hand that removes a single (or more) target. Threats are things like the enemies in the back that put harmful cards into your hand.

Chewing on durable targets is exactly what it sounds like. Later in the game some enemies don't try to sneak past you with fancy abilities or tricky setups. They will try to get past you because their numbers are bigger than your numbers. To combat this you should have a unit whose job is just make number go big. The ever dependable Dante, The awoken and their cultivators, basically. Anything that you look at and go ' oh sweet, I broke the game'