See "Gladiator Beast Alexander" for additional rulings.
If “Gladiator Beast Secutor” attacks or is attacked and it is flipped face-down or removed from the field before the end of the Battle Phase, it will not be able to activate its effect to Special Summon 2 “Gladiator Beast” monsters from the Deck, even if it is returned to the field or flipped face-up before the end of the Battle Phase.
When you activate the effect of “Gladiator Beast Secutor” and you have only 1 available Monster Zone Space, you will still choose 2 “Gladiator Beast” monsters. You will choose one of the selected monsters and Special Summon it, and the other is destroyed and sent to the Graveyard.
If you activate the effect of “Gladiator Beast Secutor” and when resolving the effect you only have 1 “Gladiator Beast” monster that you can Special Summon, the effect of “Gladiator Beast Secutor” disappears and you will verify with your opponent by briefly revealing your Deck.