A deck has 60 cards after all, which leaves you plenty of room to squeeze in two or even three different themes
Legality depends on the tournament format -- The Nipton Lottery can be legal in some formats and banned or restricted in others
Some of these crossovers have been more significant than others: the first major Universes Beyond release was the Tales of Middle-earth set released back in 2023, an entire Lord of the Rings -themed expansion
Similarly, if an effect attempts to put a modal double-faced card onto the battlefield transformed, it will enter transformed if its back face has a permanent type
There are only a few slots for random off-theme creatures, so use those sparingly
The rest of this guide focuses primarily on the above-bulk and bulk rare tiers, because that's where the biggest gap exists between what most people do (dump it all for buylist prices) and what they could be doing