They allow you to cast spells that cost four or more mana from the top of your library
The fact that this card can be played for only two mana is an excellent bonus, allowing you to surprise your opponent
Just picture a giant ape showing up and smashing a random object in your home
Seasoned Hallowblade can get indestructible by discarding a card from your hand, or you can cast a spell like Fight as One to give a creature or two indestructible until end of turn
In Standard, I think this otter wizard will be viable in a future Izzet turns deck if WoTC hasnt learned and keeps printing those cards
For 4 mana, we get a game-ender for 2 mana cheaper than Felidar Sovereign on a white enchantment, so it's harder to remove with just a simple Doom Blade, and doesnt require we spend that 50 life to blast someone like Aetherflux Reservoir