Can i manually remove from play any cards i want like "Insect Knight" to special summon cards like Doom Dozer

Question

or i have to use a card effects or spell, traps to do it?

Answer 1

Doom Dozer

Rare

This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except by removing from play 2 Insect-Type monsters in your Graveyard. When this card inflicts Battle Damage to your opponent's Life Points, send 1 card from the tops of your opponent's Deck to the Graveyard.

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Remove from graveyard. Yes manually remove them.. the 2insect cards have to be legally in the graveyard first though

Answer 2

you remove 2 insects in your graveyard with doom dozer's effect to summon it. if you use soul release to remove 2 insects in your graveyard while doom dozer is in your hand, you can't summon it because they weren't removed with dozer's effect