If your opponent loses the game after you declare attackers but before the melee trigger itself resolves (say, they were already at 3 life and someone Lightning Bolts them), the melee buff will still count that opponent as someone youve attacked this combat. What does matter is that you have to declare the attack for it to count towards the melee buff
Then there are the game-impacting oversized cards, such as Vanguard cards
TypeEnchantment Creature Saga Moogle Collector Number194 Rarityrare ArtistMinoru (As this Saga enters and after your draw step, add a lore counter
It can come down on its own in the late game and take over a board state, creating an army of squirrels outright or turning an existing army into finishers
While its very vulnerable to cards like Irohs Demonstration, I expect Dimir Midrange players to find slots for this one regardless
Condition is a huge factor for this card, as most MP or worse copies will max out at $250, while near-mint copies can command anywhere between $350 to $500, depending on how good the condition is, as a highly-graded copy sells for more than $500