A 2/4 is pretty mediocre for four mana in this day and age, and its ability seems very non-tricky because it is always face-up on the table
"Or less." If you control just it, then you cannot drop a lesser drop, just a three-drop
Its still something desired by many players, and played a lot
You can simply use cards like Infectious Inquiry and Vraska's Fall to spread poison around and sit behind your massive creatures while proliferate cards like Vraska, Betrayal's Sting and Evolution Sage slowly kill your opponents
What would you like to see in new Thallid cards
(This includes manifest, disguise, cloak, morph, and a few older effects that turn cards face down.) Common methods for doing this include using markers or dice, or simply placing them in order on the battlefield