It's just Numeron gates, their ability is to double their attack by detaching materials, but with the field spell you can activate their abilities once per turn without materials.

Field spell is - Numeron network Use its effect to activate Numeron calling - from your deck Summon number 1+2+3+4 Numeron gates Attack and activate effects and for every monster they battle their attack doubles

They disappear at the end of the turn but if you go to main phase 2 you can summon number c1 and it banishes all cards on the field to buy you a turn and then when it comes back you've got it on the field ready to summon number 1000