Whenever they enter the battlefield or attack, you can venture into the dungeon
If you think of this as a Frogmite where you have to pay 1UG to draw and play a random card from your deck it sounds a lot less value, more like a Think Twice
If you're sticking to the Vampire Aristocrats theme then the first cards I'd pick up would be Vampiric Tutor (finds Skullclamp and has Vampire in it!), Bloodletter of Aclazotz which doubles your drain / damage output on your turn absolutely wild, Bloodline Keeper provides sac fodder and a strong anthem, Legion's Landing nice thematic ramp, and Sorin, Imperious Bloodlord thematic ramp and removal
Pinnacle Emissary will create a Drone for each artifact you cast and, since Drix Interlacer cares about artifacts entering, it will essentially get two counters for every artifact you cast
Splitting Slime: this is a very easy card to turn monstrous
With cards like Perona and the blocker Doflamingo, you can rearrange the top of your deck to guarantee your free characters every time your leader attacks