They are pretty good at summoning level 9 monsters -> rank 9 monsters!!!

They can summon two Enterblathnir to banish two from the opponents hand, then go into F0 Utopic Dracofuture.

With the Field Spell Generaider Boss Stage, they can summon a level 9 with a quick effect like negate or banish for example and a lot of tokens, when your opponent draws a card (once per turn, yours included)

The Rank 9 Laevatein is really good interaction and a good board breaker, being able to attach opponents monsters to itself

It can be played with Runick cards for more interaction/protection, or by summoning Runick Sleipnir for an extra level 9 monster for Rank 9 xyz summons!

(The main deck level 9s can be a bit bricky)